LTC4120/LTC4120-4.2
1
Rev. G
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TYPICAL APPLICATION
FEATURES DESCRIPTION
Wireless Power Receiver and
400mA Buck Battery Charger
The LTC
®
4120 is a constant-current/constant-voltage wire-
less receiver and battery charger. An external program-
ming resistor sets the charge current up to 400mA. The
LTC4120-4.2 is suitable for charging Li-Ion/Polymer batter-
ies, while the programmable float voltage of the LTC4120
accommodates several battery chemistries. The LTC4120
uses a Dynamic Harmonization Control (DHC) technique that
allows high efficiency contactless charging across an air gap.
The LTC4120 regulates its input voltage via the DHC pin.
This technique modulates the resonant frequency of a
receiver tank to automatically adjust the power received
as well as the power transmitted to provide an efficient
solution for wirelessly charging battery-powered devices.
Wireless charging with the LTC4120 provides a method
to power devices in harsh environments without requiring
expensive failure-prone connectors. This allows products
to be charged while locked within sealed enclosures, or
in moving or rotating equipment, or where cleanliness or
sanitation is critical.
This full featured battery charger includes accurate RUN
pin threshold, low voltage battery preconditioning and bad
battery fault detection, timer termination, auto-recharge,
and NTC temperature qualified charging. The FAULT pin
provides an indication of bad battery or temperature faults.
Once charging is terminated, the LTC4120 signals end-of-
charge via the CHRG pin, and enters a low current sleep
mode. An auto-restart feature starts a new charging cycle
if the battery voltage drops by 2.2%.
APPLICATIONS
n Dynamic Harmonization Control Optimizes
Wireless Charging Over a Wide Coupling Range
n Wide Input Voltage Range (12.5V to 40V)
n Adjustable Float Voltage (3.5V to 11V)
n Fixed 4.2V Float Voltage Option (LTC4120-4.2)
n 50mA to 400mA Charge Current Programmed with a
Single Resistor
n ±1% Feedback Voltage Accuracy
n Programmable 5% Accurate Charge Current
n No Microprocessor Required
n No Transformer Core
n Thermally Enhanced, Low Profile 16-Lead
(3mm × 3mm × 0.75mm) QFN Package
n Handheld Instruments
n Industrial/Military Sensors and Devices
n Harsh Environments
n Portable Medical Devices
n Physically Small Devices
n Electrically Isolated Devices
All registered trademarks and trademarks are the property of their respective owners.
+
INTVCC
IN
FREQRUN
BOOST
SW
CHGSNS
NTC
DHC
FAULT
CHRG
3.01k 22µF
T
4120 TA01a
Li-Ion
4.2V
22nF
26.7nF
6.5nF
47µH5µH
Tx CIRCUITRY
10µF
2.2µF
33µH
FB
PROG FBG
LTC4120
GND
BAT
1.01M
1.35M
Wireless Rx Voltage/Charge Current vs Spacing
SPACING (cm)
0.4
VIN(RX) (V)
CHARGE CURRENT (mA)
30
35
40
1.0 1.4
4120 TA01b
25
20
0.6 0.8 1.2 1.6 1.8
VIN
15
10
200
267
333
400
133
67
0
ICHARGE
MAX
NOT
CHARGING
CHARGING
LTC4120/LTC4120-4.2
2
Rev. G
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PIN CONFIGURATION
ABSOLUTE MAXIMUM RATINGS
IN, RUN, CHRG, FA U LT, DHC ...................... –0.3V to 43V
BOOST ................................... VSW – 0.3V to (VSW + 6V)
SW (DC) ........................................ –0.3V to (VIN + 0.3V)
SW (Pulsed <100ns) ......................–1.5V to (VIN + 1.5V)
CHGSNS, BAT, FBG, FB ...............................–0.3V to 12V
FREQ, NTC, PROG, INTVCC .......................... –0.3V to 6V
ICHGSNS, IBAT ..................................................... ±600mA
(Note 1)
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC4120EUD#PBF LTC4120EUD#TRPBF LGHB 16-Lead (3mm × 3mm) Plastic QFN –40°C to 125°C
LTC4120IUD#PBF LTC4120IUD#TRPBF LGHB 16-Lead (3mm × 3mm) Plastic QFN –40°C to 125°C
LTC4120EUD-4.2#PBF LTC4120EUD-4.2#TRPBF LGMT 16-Lead (3mm × 3mm) Plastic QFN –40°C to 125°C
LTC4120IUD-4.2#PBF LTC4120IUD-4.2#TRPBF LGMT 16-Lead (3mm × 3mm) Plastic QFN –40°C to 125°C
Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.
LTC4120 OPTIONS FLOAT VOLTAGE
LTC4120 Programmable
LTC4120-4.2 4.2V Fixed
LTC4120 LTC4120-4.2
16 15 14 13
5 6 7 8
TOP VIEW
17
GND
UD PACKAGE
16-LEAD (3mm × 3mm) PLASTIC QFN
TJMAX = 125°C, θJA = 54°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB TO OBTAIN
θ
JA
9
10
11
12
4
3
2
1INTVCC
BOOST
IN
SW
NTC
FBG
FB
BAT
RUN
FAULT
CHRG
PROG
GND
DHC
FREQ
CHGSNS
16 15 14 13
5 6 7 8
TOP VIEW
17
GND
UD PACKAGE
16-LEAD (3mm × 3mm) PLASTIC QFN
TJMAX = 125°C, θJA = 54°C/W
EXPOSED PAD (PIN 17) IS GND, MUST
BE SOLDERED TO PCB TO OBTAIN θ
JA
9
10
11
12
4
3
2
1INTVCC
BOOST
IN
SW
NTC
NC
BATSNS
BAT
RUN
FAULT
CHRG
PROG
GND
DHC
FREQ
CHGSNS
IDHC ...............................................................350mARMS
ICHRG, IFAU LT, IFBG ..................................................±5mA
IFB .........................................................................±5mA
IINTVCC .................................................................. –5mA
Operating Junction Temperature Range
(Note 2) .................................................. –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
LTC4120/LTC4120-4.2
3
Rev. G
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ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = VRUN = 15V, VCHGSNS = VBAT = 4V, RPROG = 3.01k,
VFB = 2.29V (LTC4120), VBATSNS = 4V (LTC4120-4.2). Current into a pin is positive out of the pin is negative.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Operating Input Supply Range l12.5 40 V
Battery Voltage Range 0 11 V
IIN DC Supply Current Switching, FREQ = GND 3.5 mA
Standby Mode (Note 3) l130 220 µA
Sleep Mode (Note 3)
LTC4120: VFB = 2.51V (Note 5),
LTC4120-4.2: VBATSNS = 4.4V
l
60
100
µA
Disabled Mode (Note 3) l37 70 µA
Shutdown Mode (Note 3) l20 40 µA
∆VDUVLO Differential Undervoltage Lockout VIN-VBAT Falling, VIN = 5V (LTC4120),
VIN-VBATSNS Falling, VIN = 5V (LTC4120-4.2)
l20 80 160 mV
Hysteresis VIN-VBAT Rising, VIN = 5V (LTC4120),
VIN-VBATSNS Rising, VIN = 5V (LTC4120-4.2) 115 mV
UVINTVCC INTVCC Undervoltage Lockout INTVCC Rising, VIN = INTVCC + 100mV, VBAT = NC l4.00 4.15 4.26 V
Hysteresis INTVCC Falling (Note 4) 220 mV
Battery Charger
IBAT BAT Standby Current Standby Mode (LTC4120) (Notes 3, 7, 8)
Standby Mode (LTC4120-4.2) (Notes 3, 7, 8)
l
l
2.5
50 4.5
1000 µA
nA
BAT Shutdown Current Shutdown Mode (LTC4120) (Notes 3, 7, 8)
Shutdown Mode (LTC4120-4.2) (Notes 3, 7, 8)
l
l
1100
10 2000
1000 nA
nA
IBATSNS BATSNS Standby Current (LTC4120-4.2) Standby Mode (Notes 3, 7, 8) l5.4 10 µA
BATSNS Shutdown Current (LTC4120-4.2) Shutdown Mode (Notes 3, 7, 8) l1100 2000 nA
IFB Feedback Pin Bias Current (LTC4120) VFB = 2.5V (Notes 5, 7) l25 60 nA
IFBG(LEAK) Feedback Ground Leakage Current (LTC4120) Shutdown Mode (Notes 3, 7) l1 µA
RFBG Feedback Ground Return Resistance (LTC4120)l1000 2000 Ω
VFB(REG) Feedback Regulation Voltage (LTC4120) (Note 5)
l
2.393
2.370 2.400 2.407
2.418 V
V
VFLOAT Regulated Float Voltage (LTC4120-4.2)
l
4.188
4.148 4.200 4.212
4.227 V
V
ICHG Battery Charge Current RPROG = 3.01k
RPROG = 24.3k
l
l
383
45 402
50 421
55 mA
mA
VUVCL Undervoltage Current Limit VIN Falling 12.0 V
VRCHG Battery Recharge Threshold VFB Falling Relative to VFB_REG (LTC4120) (Note 5) l–38 –50 –62 mV
VRCHG_4.2 Battery Recharge Threshold VBATSNS Falling Relative to VFLOAT (LTC4120-4.2) l–70 –92 –114 mV
hPROG Ratio of BAT Current to PROG Current VTRKL < VFB < VFB(REG) (LTC4120) (Note 5)
VTRKL_4.2 < VBATSNS < VFLOAT (LTC4120-4.2) 988 mA/mA
VPROG PROG Pin Servo Voltage l1.206 1.227 1.248 V
RSNS CHGSNS-BAT Sense Resistor IBAT = –100mA 300 mΩ
LTC4120/LTC4120-4.2
4
Rev. G
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ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = VRUN = 15V, VCHGSNS = VBAT = 4V, RPROG = 3.01k,
VFB = 2.29V (LTC4120), VBATSNS = 4V (LTC4120-4.2). Current into a pin is positive out of the pin is negative.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
ILOWBAT Low Battery Linear Charge Current 0V < VFB < VTRKL, VBAT = 2.6V (LTC4120),
VBATSNS < VTRKL_4.2, VBAT = 2.6V (LTC4120-4.2) 6 9 16 mA
VLOWBAT Low Battery Threshold Voltage VBAT Rising (LTC4120),
VBATSNS Rising (LTC4120-4.2)
l2.15 2.21 2.28 V
Hysteresis 147 mV
ITRKL Switch Mode Trickle Charge Current VLOWBAT < VBAT, VFB < VTRKL (LTC4120) (Note 5),
VLOWBAT < VBATSNS < VTRKL_4.2 (LTC4120-4.2) ICHG/10 mA
PROG Pin Servo Voltage in Switch Mode
Trickle Charge VLOWBAT < VBAT, VFB < VTRKL (LTC4120) (Note 5),
VLOWBAT < VBATSNS < VTRKL_4.2 (LTC4120-4.2) 122 mV
VTRKL Trickle Charge Threshold VFB Rising (LTC4120) (Note 5) l1.64 1.68 1.71 V
Hysteresis VFB Falling (LTC4120) (Note 5) 50 mV
VTRKL_4.2 Trickle Charge Threshold VBATSNS Rising (LTC4120-4.2) l2.86 2.91 2.98 V
Hysteresis VBATSNS Falling (LTC4120-4.2) 88 mV
hC/10 End of Charge Indication Current Ratio (Note 6) 0.1 mA/mA
Safety Timer Termination Period 1.3 2.0 2.8 Hours
Bad Battery Termination Timeout 19 30 42 Minutes
Switcher
fOSC Switching Frequency FREQ = INTVCC
FREQ = GND
l
l
1.0
0.5 1.5
0.75 2.0
1.0 MHz
MHz
tMIN(ON) Minimum Controllable On-Time (Note 9) 120 ns
Duty Cycle Maximum (Note 9) 94 %
Top Switch RDS(ON) ISW = –100mA 0.8 Ω
Bottom Switch RDS(ON) ISW = 100mA 0.5 Ω
IPEAK Peak Current Limit Measured Across RSNS with a 15µH Inductor in
Series with RSNS (Note 9) 585 750 1250 mA
ISW Switch Pin Current (Note 8) VIN = Open-Circuit, VRUN = 0V, VSW = 8.4V (LTC4120)
VIN = Open-Circuit, VRUN = 0V, VSW = 4.2V
(LTC4120-4.2)
l
l
15
730
15 µA
µA
Status Pins FAULT, CHRG
Pin Output Voltage Low I = 2mA 500 mV
Pin Leakage Current V = 43V, Pin High Impedance 0 1 µA
NTC
Cold Temperature VNTC/VINTVCC Fault Rising VNTC Threshold
Falling VNTC Threshold
l73 74
72 75
%INTV
CC
%INTV
CC
Hot Temperature VNTC/VINTVCC Fault Falling VNTC Threshold
Rising VNTC Threshold
l35.5 36.5
37.5 37.5
%INTV
CC
%INTV
CC
NTC Disable Voltage Falling VNTC Threshold
Rising VNTC Threshold
l1 2
33
%INTV
CC
%INTV
CC
NTC Input Leakage Current VNTC = VINTVCC –50 50 nA
LTC4120/LTC4120-4.2
5
Rev. G
For more information www.analog.com
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = VRUN = 15V, VCHGSNS = VBAT = 4V, RPROG = 3.01k,
VFB = 2.29V (LTC4120), VBATSNS = 4V (LTC4120-4.2). Current into a pin is positive out of the pin is negative.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
RUN
VEN Enable threshold VRUN Rising l2.35 2.45 2.55 V
Hysteresis VRUN Falling 200 mV
Run Pin Input Current VRUN = 40V 0.01 0.1 µA
VSD Shutdown Threshold (Note 3) VRUN Falling l0.4 1.2 V
Hysteresis 220 mV
FREQ
FREQ Pin Input Low l0.4 V
FREQ Pin Input High VINTVCC-VFREQ l0.6 V
FREQ Pin Input Current 0V < VFREQ < VINTVCC ±1 µA
Dynamic Harmonization Control
VIN(DHC) Input Regulation Voltage 14 V
DHC Pin Current VDHC = 1V, VIN < VIN(DHC) 330 mARMS
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTC4120 is tested under pulsed load conditions such that
TJ ≈ TA. The LTC4120E is guaranteed to meet performance specifications
for junction temperatures from 0°C to 85°C. Specifications over the
–40°C to 125°C operating junction temperature range are assured by
design, characterization and correlation with statistical process controls.
The LTC4120I is guaranteed over the full –40°C to 125°C operating
junction temperature range. Note that the maximum ambient temperature
consistent with these specifications is determined by specific operating
conditions in conjunction with board layout, the rated package thermal
impedance, and other environmental factors.
Note 3: Standby mode occurs when the LTC4120 stops switching due
to an NTC fault condition, or when the charge current has dropped low
enough to enter Burst Mode operation. Disabled mode occurs when VRUN
is between VSD and VEN. Shutdown mode occurs when VRUN is below VSD
or when the differential undervoltage lockout is engaged. SLEEP mode
occurs after a timeout while the battery voltage remains above the VRCHG
or VRCHG_42 threshold.
Note 4: The internal supply INTVCC should only be used for the NTC
divider, it should not be used for any other loads.
Note 5: The FB pin is measured with a resistance of 588k in series with
the pin.
Note 6: hC/10 is expressed as a fraction of measured full charge current as
measured at the PROG pin voltage when the CHRG pin de-asserts.
Note 7: In an application circuit with an inductor connected from SW
to CHGSNS, the total battery leakage current when disabled is the sum
of IBAT, IFBG(LEAK) and ISW (LTC4120), or IBATSNS and IBAT and ISW
(LTC4120-4.2).
Note 8: When no supply is present at IN, the SW powers IN through
the body diode of the topside switch. This may cause additional SW pin
current depending on the load present at IN.
Note 9: Guaranteed by design and/or correlation to static test.
ELECTRICAL CHARACTERISTICS
LTC4120/LTC4120-4.2
6
Rev. G
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TYPICAL PERFORMANCE CHARACTERISTICS
Typical VFB(REG) vs Temperature
IN Pin Disabled/Shutdown Current
vs Temperature
BAT Pin Sleep/Shutdown Current
vs Temperature
Typical Battery Charge Current
vs Temperature
Typical VFLOAT vs Temperature
LTC4120-4.2
IN Pin Standby/Sleep Current vs
Temperature
TA = 25°C, unless otherwise noted.
TEMPERATURE (°C)
–40
2.36
VFB(REG) (V)
2.37
2.39
2.40
2.41
2.43
–25 35 65
4120 G01
2.38
2.42
20 95 125
DUT = DEVICE
UNDER TEST
110
–10 550 80
4 UNITS TESTED
HIGH LIMIT
DUT1 VFB(REG) (V)
DUT2 VFB(REG) (V)
DUT3 VFB(REG) (V)
DUT4 VFB(REG) (V)
LOW LIMIT
TEMPERATURE (°C)
4.15
4.16
4.17
4.18
4.19
V
FLOAT
(V)
4.25
4.24
4.23
4.22
4.21
4.20
4120 G20
4 UNITS TESTED
HIGH LIMIT
DUT1 V
FLOAT
DUT2 V
FLOAT
DUT3 V
FLOAT
DUT4 V
FLOAT
LOW LIMIT
–40 5 20 35 958065
–25 –10 50 110 125
TEMPERATURE (°C)
–50
120
140
180
25 75
4120 G02
100
80
–25 0 50 100 125
60
40
160
IIN (µA)
2 UNITS TESTED
VIN = 15V
IIN STANDBY FREQ = INTVCC
IIN STANDBY FREQ = INTVCC
IIN STANDBY FREQ = GND
IIN STANDBY FREQ = GND
IIN SLEEP
IIN SLEEP
TEMPERATURE (°C)
–50
IIN (µA)
40
50
60
25 75
4120 G03
30
20
–25 0 50 100 125
10
0
IIN SD
IIN SD
IIN DISABLED
IIN DISABLED
2 UNITS TESTED
VIN = 15V
TEMPERATURE (°C)
–50
IBAT (µA)
7
25
4120 G04
4
2
–25 0 50
1
0
8
6
5
3
75 100 125
IBAT SLEEP
IBAT SLEEP
IBAT SHUTDOWN
IBAT SHUTDOWN
2 UNITS TESTED
VBAT = 4.2V
RFB2 = 1.01M
RFB1 = 1.35M
TEMPERATURE (°C)
–50
399
400
402
25 75
398
397
–25 0 50 100 125
396
395
401
ICHG (mA)
FREQ = GND
FREQ = GND
FREQ = INTVCC
FREQ = INTVCC
RPROG = 3.01k
2 UNITS TESTED
Typical RSNS Current Limit
vs Temperature
TEMPERATURE (°C)
–50
I
PEAK
(mA)
125
4120 G06
1080
1100
1060
1040
980
1000
960
940
920
1020
050 100
–25 25 75
1120
DUT1
DUT2
DUT3
3 UNITS TESTED
LTC4120/LTC4120-4.2
7
Rev. G
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Switching Frequency
vs Temperature Buck Efficiency vs Battery Current
TEMPERATURE (°C)
–50
0.8
1.0
1.4
25 75
4120 G07
0.6
–25 0 50 100 125
0.4
0.2
0
1.2
fOSC (MHz)
FREQ = GND
FREQ = GND
FREQ = INTVCC
FREQ = INTVCC
2 UNITS TESTED
IBAT (mA)
0
EFFICIENCY (%)
75
80
85
400
4120 G08
70
65
60
50 100 200 300
50 150 250 350
55
95
90
VIN = 12.5V
VIN = 14V
VIN = 20V
VIN = 30V
LSW = 68µH, SLF12555T-680M1R3
FREQ = GND
VBAT = 4.2V
Burst Mode Trigger Current
Typical Burst Mode Waveforms,
IBAT = 38mA
Typical tMIN(ON) vs Temperature
TYPICAL PERFORMANCE CHARACTERISTICS
Wireless Power Transfer Efficiency,
VIN_RX vs Battery Current
BAT Pin Leakage Current/VBAT -VIN
vs Temperature
Typical Wireless Charging Cycle
TA = 25°C, unless otherwise noted.
TEMPERATURE (°C)
–50
IBAT (µA)
VBAT-VIN (mV)
14
25
4120 G09
8
4
–25 0 50
2
0
16
12
10
6
350
200
100
50
0
400
300
250
150
75 100 125
IBAT
IBAT
VBAT-VIN
VBAT-VIN
2 UNITS TESTED
VIN = OPEN-CIRCUIT
VBAT = 4.2V
TEMPERATURE (°C)
–50
80
tMIN(0N) (ns)
85
95
100
105
130
115
050 75 100
4120 G10
90
120
125
110
–22 25 125
2 UNITS TESTED
IBAT (mA)
0
50
60
70
200
4120 G11
40
30
50 100 150 250
20
10
0
20
22
24
18
16
14
12
10
EFFICIENCY (%)
VIN_RX (V)
9mm EFFICIENCY
10mm EFFICIENCY
11mm EFFICIENCY
9mm V_RX
10mm V_RX
11mm V_RX
VFLOAT = 8.3V
LSW = SLF6028-470MR59
RPROG = 4.64k
TIME (HOURS)
0
0
BATTERY CURRENT (mA)
VBAT, VCHRG (V)
50
150
200
250
450
4120 G12
100
2
13
300
350
400
0
0.5
1.5
2.0
2.5
4.5
1.0
3.0
3.5
4.0
VCHRG
VBAT
IBAT
BAT = 940mAhr
LSW = TDK SLF4075 15µH
RFB1 = 732k, RFB2 = 976k
RPROG = 3.01k
APPLICATION CCT OF FIGURE 10
SPACING = 14mm
VIN (V)
10
0
IBAT (mA)
10
30
40
50
30
90
4120 G13
20
20
15 35
25 40
60
70
80
RPROG = 6.2k
RPROG = 3k
VSW
5V/DIV
VPROG
500mV/DIV
ILSW
200mA/DIV 0mA
0V
0V
4µs/DIV 4120 G14
LTC4120/LTC4120-4.2
8
Rev. G
For more information www.analog.com
IN Pin Standby Current vs VIN
IN Pin Disabled Current
vs Input Voltage UVCL: ICHARGE vs Input Voltage
IN Pin Shutdown Current
vs Input Voltage
IN Pin Switching Current vs Input
Voltage
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise noted.
VIN (V)
0
IIN (µA)
160
180
200
30 3515 20 25
4120 G15
140
120
5 10 40
100
80
220 VBAT = 4.21V
NTC = GND
IIN STBY FREQ HIGH 130°C
IIN STBY FREQ LOW 130°C
IIN STBY FREQ HIGH 25°C
IIN STBY FREQ LOW 25°C
IIN STBY FREQ HIGH –45°C
IIN STBY FREQ LOW –45°C
VIN (V)
0
IIN (µA)
40
50
60
40
4120 G16
30
20
010 20 30
10
80
70
IIN SD TEMP = 125°C
IIN SD TEMP = 35°C
IIN SD TEMP = –40°C
VRUN = 0.4V
VIN (V)
0
0
IIN (µA)
10
30
40
50
100
70
10 20
4120 G17
20
80
90
60
30 40
IIN SD TEMP = 125°C
IIN SD TEMP = 35°C
IIN SD TEMP = –40°C
VRUN = 1.6V
VIN (V)
10
4
5
7
20 30
4120 G18
3
2
15 25 35 40
1
0
6
IIN (mA)
UVCL IBAT = 0
130°C 25°C –45°C
IICCQ(SWITCHING) FREQ HIGH
FREQ = INTVCC
IICCQ(SWITCHING) FREQ LOW
FREQ = GND
VIN (V)
11.90
ICHARGE (mA)
0.20
4120 G19
0.10
012.00 12.10
11.95 12.05 12.15
0.30
0.40
0.15
0.05
0.25
0.35
12.20
IBAT TEMP = 125°C
IBAT TEMP = 35°C
IBAT TEMP = –40°C
LTC4120/LTC4120-4.2
9
Rev. G
For more information www.analog.com
PIN FUNCTIONS
INTVCC (Pin 1): Internal Regulator Output Pin. This pin is
the output of an internal linear regulator that generates the
internal INTVCC supply from IN. It also supplies power to
the switch gate drivers and the low battery linear charge
current ILOWBAT. Connect a 2.2µF low ESR capacitor from
INTVCC to GND. Do not place any external load on INTVCC
other than the NTC bias network. Overloading this pin can
disrupt internal operation. When the RUN pin is above
VEN, and INTVCC rises above the UVLO threshold, and
IN rises above BAT by ∆VDUVLO and its hysteresis, the
charger is enabled.
BOOST (Pin 2): Boosted Supply Pin. Connect a 22nF
boost capacitor from this pin to the SW pin.
IN (Pin 3): Positive Input Power Supply. Decouple to GND
with a 10µF or larger low ESR capacitor.
SW (Pin 4): Switch Pin. The SW pin delivers power from
IN to BAT via the step-down switching regulator. An
inductor should be connected from SW to CHGSNS. See
the Applications Information section for a discussion of
inductor selection.
GND (Pin 5, Exposed Pad Pin 17): Ground Pin. Connect
to exposed pad. The exposed pad must be soldered to
PCB GND to provide a low electrical and thermal imped-
ance connection to ground.
DHC (Pin 6): Dynamic Harmonization Control Pin.
Connect a Schottky diode from the DHC pin to the IN pin,
and a capacitor from the DHC pin as shown in the Typical
Application or the Block Diagram. When VIN is greater
than V
IN(DHC)
, this pin is high impedance. When V
IN
is
below VIN(DHC) this pin is low impedance allowing the
LTC4120 to modulate the resonance of the tuned receiver
network. See Applications Information for more informa-
tion on the tuned receiver network.
FREQ (Pin 7): Buck Switching Frequency Select Input Pin.
Connect to INTVCC to select a 1.5MHz switching frequency
or GND to select a 750kHz switching frequency. Do not float.
CHGSNS (Pin 8): Battery Charge Current Sense Pin. An
internal current sense resistor between CHGSNS and BAT
pins monitors battery charge current. An inductor should
be connected from SW to CHGSNS.
BAT (Pin 9): Battery Output Pin. Battery charge current is
delivered from this pin through the internal charge current
sense resistor. In low battery conditions a small linear
charge current, ILOWBAT, is sourced from this pin to pre-
condition the battery. Decouple the BAT pin with a low
ESR 22µF or greater ceramic capacitor to GND.
BATSNS (Pin 10, LTC4120-4.2 Only): Battery Voltage
Sense Pin. For proper operation, this pin must always be
connected physically close to the positive battery terminal.
FB (Pin 10, LTC4120 Only): Battery Voltage Feedback Pin.
The charge function operates to achieve a final float voltage
of 2.4V at this pin. Battery float voltage is programmed
using a resistive divider from BAT to FB to FBG, and can be
programmed up to 11V. The feedback pin input bias cur-
rent, IFB, is 25nA. Using a resistive divider with a Thevenin
equivalent resistance of 588k compensates for input bias
current error (see curve of FB Pin Bias Current versus
Temperature in the Typical Performance Characteristics).
FBG (Pin 11, LTC4120 Only): Feedback Ground Pin.
This pin disconnects the external FB divider load from
the battery when it is not needed. When sensing the bat-
tery voltage this pin presents a low resistance, RFBG, to
GND. When in disabled or shutdown modes this pin is
high impedance.
NTC (Pin 12): Input to the Negative Temperature Coefficient
Thermistor Monitoring Circuit. The NTC pin connects to
a negative temperature coefficient thermistor which is
typically co-packaged with the battery to determine if the
battery is too hot or too cold to charge. If the battery’s
temperature is out of range, the LTC4120 enters standby
mode and charging is paused until the battery tempera-
ture re-enters the valid range. A low drift bias resistor is
required from INTVCC to NTC and a thermistor is required
from NTC to GND. Tie the NTC pin to GND to disable NTC
qualified charging if NTC functionality is notrequired.
PROG (Pin 13): Charge Current Program and Charge
Current Monitor Pin. Connect a 1% resistor between
3.01k (400mA) and 24.3k (50mA) from PROG to ground
to program the charge current. While in constant-current
mode, this pin regulates to 1.227V. The voltage at this pin
represents the average battery charge current using the
following formula:
IBAT =hPROG •
V
PROG
R
PROG
LTC4120/LTC4120-4.2
10
Rev. G
For more information www.analog.com
PIN FUNCTIONS
where hPROG is typically 988. Keep parasitic capacitance
on the PROG pin to a minimum.
CHRG (Pin 14): Open-Drain Charge Status Output Pin.
Typically pulled up through a resistor to a reference volt-
age, the CHRG pin indicates the status of the battery char-
ger. The pin can be pulled up to voltages as high as IN
when disabled, and can sink currents up to 5mA when
enabled. When the battery is being charged, the CHRG
pin is pulled low. When the termination timer expires or
the charge current drops below 10% of the programmed
value, the CHRG pin is forced to a high impedance state.
FAULT (Pin 15): Open-Drain Fault Status Output Pin.
Typically pulled up through a resistor to a reference volt-
age, this status pin indicates fault conditions during a
charge cycle. The pin can be pulled up to voltages as high
as IN when disabled, and can sink currents up to 5mA
when enabled. An NTC temperature fault causes this pin
to be pulled low. A bad battery fault also causes this pin
to be pulled low. If no fault conditions exist, the FAULT
pin remains high impedance.
RUN (Pin 16): Run Pin. When RUN is pulled below VEN
and its hysteresis, the device is disabled. In disabled
mode, battery charge current is zero and the CHRG and
FAULT pins assume high impedance states. If the voltage
at RUN is pulled below V
SD
, the device is in shutdown
mode. When the voltage at the RUN pin rises above VEN,
the INTVCC LDO turns on. When the INTVCC LDO rises
above its UVLO threshold the charger is enabled. The
RUN pin should be tied to a resistive divider from VIN to
program the input voltage at which charging is enabled.
Do not float the RUN pin.
INTVCC
ITH
INTVCC
INTVCC
HOT
COLD
DISABLE
IN
2
INTVCC
INTVCC
INTVCC
RSNS
0.3Ω
RFB1
10k
RNOM
10k
T
RFB2
RPROG
4
PWM
LTC4120
ENABLE
ENABLE
RUN
CIN
10µF
•
C2S
C2P
LR
2.45V
BOOST
CINTVCC
2.2µF
CBST
22nF
LSW
33µH
1
INTVCC
SW
8
CHGSNS
10
FB
11
FBG
13
PROG
4120 F01
9
BAT
GND
CBAT
22µF
Li-Ion
LDO
5
+
–
INTVCC
588k
V-EA
C-EA
UVCL
DZ
VFB(REG)
1.2V
ENABLE
+
–
+
–+
+
–
0.9V
BAT
SHUTDOWN
DUVLO
VIN(DHC)
IN
+
–
IN – 80mV
+
–
BAT
2.21V
+
–
16
DHC
6
FAULT
ENABLE
LOWBAT
15
CHRG
14
NTC
LOWBAT
12
FREQ
IN
IN
7
IN
3
CNTRL
NTC
DHC
Figure1. Block Diagram
BLOCK DIAGRAM
LTC4120/LTC4120-4.2
11
Rev. G
For more information www.analog.com
BLOCK DIAGRAM
INTVCC
ITH
IN
INTVCC
RSNS
0.3Ω
RPROG
LTC4120-4.2
8
CHGSNS
10
BATSNS
13
PROG
4120 F02
9
BAT
CBAT
22µF
Li-Ion
+
–
INTVCC
588k
V-EA
C-EA
UVCL
DZ
VFB(REG)
1.2V
ENABLE
+
–
+
–
+
BATSNS DUVLO
IN – 80mV
+
–
BATSNS
2.21V
+
–
LOWBAT
Figure2. LTC4120-4.2 BATSNS Connections
TEST CIRCUIT
NTC
VIN(DHC)
INTVCC
IN
RUN
2.2µF
4120 F03
GNDDHC
LTC4120
10µF
10Ω
665Ω
49.9Ω
IRLML5103TR
665Ω
2k
20V
680nF
Figure3. VIN(DHC) Test Circuit
LTC4120/LTC4120-4.2
12
Rev. G
For more information www.analog.com
OPERATION
Wireless Power System Overview
The LTC4120 is one component in a complete wireless
power system. A complete system is composed of trans-
mit circuitry, a transmit coil, a receive coil and receive
circuitry—including the LTC4120. Please refer to the
Applications Information section for more information
on transmit circuitry and coils. In particular, the Resonant
Transmitter and Receiver and the Alternative Transmitter
Options sections include information necessary to com-
plete the design of a wireless power system. Further
information can be found in the Applications Information
section of this document under the heading Resonant
Transmitter and Receiver, as well as in AN138: Wireless
Power Users Guide, as well as the DC1969A: wireless
power transmit and receiver demo kit and manual. The
Gerber layout files for both the Transmitter and Receiver
boards are available at the following link:
LTC4120 Evaluation Kits
LTC4120 Overview
The LTC4120 is a synchronous step-down (buck) wire-
less battery charger with dynamic harmonization control
(DHC). DHC is a highly efficient method of regulating the
received input voltage in a resonant coupled power trans-
fer application. The LTC4120 serves as a constant-current/
constant-voltage battery charger with the following built-
in charger functions: programmable charge current, pro-
grammable float voltage (LTC4120), battery precondition
with half-hour timeout, precision shutdown/run control,
NTC thermal protection, a 2-hour safety termination timer,
and automatic recharge. The LTC4120 also provides out-
put pins to indicate state of charge and fault status.
The circuit in Figure4 is a fully functional system using
a basic current-fed resonant converter for the transmit-
ter and a series resonant converter for the receiver with
the LTC4120. The LTC4125 advanced transmitter may
also be used with the LTC4120. For more information on
transmitter design refer to Application Note 138: Wireless
Power Users Guide.
Wireless Power Transfer
A wireless coupled power transfer system consists of a
transmitter that generates an alternating magnetic field,
and a receiver that collects power from that field. The
ideal transmitter efficiently generates a large alternating
current in the transmitter coil, LX. The push-pull current-
fed resonant converter, shown in Figure4, is an example
of a basic power transmitter that may be used with the
LTC4120. This transmitter typically operates at a fre-
quency of approximately 130kHz; though the operating
Figure4. DC-AC Converter, Transmit/Receive Coils, Tuned Series Resonant Receiver and AC-DC Rectifier
C4
R1
C5
CX
C2S
LXLR
L1 L2
VDC
5V TRANSMITTER
R2
D2
M1 M2
D5, D8, D9: DFLS240L
D3
D1 D4
C2P D8 D5
D9
DHC CBST
D6
39V
DFLZ39
LSW
BOOST
SW
CHGSNS
BAT
LTC4120
GND
IN
CIN
CBAT
4120 F04
Li-Ion
+
LTC4120/LTC4120-4.2
13
Rev. G
For more information www.analog.com
Figure5. Resonant Receiver Tank
CX
C2S
1:n
LXLRC2P D8 D5
D9
DHC
LTC4120
IN
CIN
4120 F05
OPERATION
frequency varies depending on the load at the receiver
and the coupling to the receiver coil. For LX = 5µH, and
CX = 300nF, the transmitter frequency is:
fO≈
1
2 • π• LX• CX
=130kHz
This transmitter typically generates an AC coil current of
about 2.5ARMS. For more information on this transmitter,
refer to AN138: Wireless Power Users Guide.
The receiver consists of a coil, LR, configured in a reso-
nant circuit followed by a rectifier and the LTC4120. The
receiver coil presents a load reflected back to the trans-
mitter through the mutual inductance between LR and
LX. The reflected impedance of the receiver may influ-
ence the operating frequency of the transmitter. Likewise,
the power output by the transmitter depends on the load
at the receiver. The resonant coupled charging system,
consisting of both the transmitter and LTC4120 charger,
provides an efficient method for wireless battery charging
as the power output by the transmitter varies automati-
cally based on the power used to charge a battery.
Dynamic Harmonization Control
Dynamic harmonization control (DHC) is a technique for
regulating the received input power in a wireless power
transfer system. DHC modulates the impedance of the
resonant receiver to regulate the voltage at the input to
the LTC4120. When the input voltage to the LTC4120 is
below the VIN(DHC) set point, the LTC4120 allows more
power to appear at the receiver by tuning the receiver
resonance closer to the transmitter resonance. If the input
voltage exceeds VIN(DHC), the LTC4120 tunes the receiver
resonance away from the transmitter, which reduces the
power available at the receiver. The amount that the input
power increases or decreases is a function of the cou-
pling, the tuning capacitor, C2P, the receiver coil, LR, and
the operating frequency.
Figure5 illustrates the components that implement the
DHC function to automatically tune the resonance of the
receiver. Capacitor C2S and inductor LR serve as a series
resonator. Capacitor C2P and the DHC pin of the LTC4120
form a parallel resonance when the DHC pin is low imped-
ance, and disconnect when the DHC pin is high imped-
ance. C2P adjusts the receiver resonance to control the
amount of power available at the input of the LTC4120.
C2P also affects power dissipation in the LTC4120 due
to the AC current being shunted by the DHC pin. For this
reason it is not recommended to apply total capacitance
in excess of 30nF at this pin.
Using DHC, the LTC4120 automatically adjusts the power
received depending on load requirements; typically the
load is battery charge current. This technique results in
significant power savings, as the power required by the
transmitter automatically adjusts to the requirements at
the receiver. Furthermore, DHC reduces the rectified volt-
age seen at the input of the LTC4120 under light load
conditions when the battery is fully charged.
LTC4120/LTC4120-4.2
14
Rev. G
For more information www.analog.com
OPERATION
The design of the resonant receiver circuit (LR, C2S
and C2P), the transmitter circuit, and the mutual induc-
tance between LX and LR determines both the maximum
unloaded voltage at the input to the LTC4120 as well as
the maximum power available at the input to the LTC4120.
The value and tolerances of these components must be
selected with care for stable operation, for this reason
it is recommended to only use components with tight
tolerances.
To understand the operating principle behind dynamic
harmonization control (DHC), consider the following sim-
plification. Here, a fixed-frequency transmitter is operat-
ing at a frequency fO = 130kHz. DHC automatically adjusts
the impedance of the receiver tuned network so as to
modulate the resonant frequency of the receiver between
fT and fD.
fT≅
1
2 • π• LR• C2P +C2S
( )
fD≅1
2 • π• LR• C2S
When the input voltage is above VIN(DHC) (typically 14V),
the LTC4120 opens the DHC pin, detuning the receiver
resonance away from the transmitter frequency f
O
, so that
less power is received. When the input voltage is below
V
IN(DHC)
, the LTC4120 shunts the DHC pin to ground,
tuning the receiver resonance closer to the transmitter
frequency so that more power is available.
For the resonant converter shown in Figure4, the operat-
ing frequency of the transmitter is not fixed, but varies
depending on the load impedance. However the basic
operating principle of DHC remains valid. For more infor-
mation on the design of the wireless power receiver reso-
nant circuit refer to the applications section.
Programming The Battery Float Voltage
For the LTC4120, the battery float voltage is programmed
by placing a resistive divider from the battery to FB and
FBG as shown in Figure6. The programmable battery
float voltage, VFLOAT, is then governed by the following
equation:
VFLOAT =VFB(REG) •RFB1 +RFB2
( )
RFB2
where VFB(REG) is typically 2.4V.
Due to the input bias current (IFB) of the voltage error amp
(V-EA), care must also be taken to select the Thevenin
equivalent resistance of R
FB1
||R
FB2
close to 588k. Start by
calculating RFB1 to satisfy the following relations:
RFB1 =VFLOAT • 588k
VFB(REG)
Find the closest 0.1% or 1% resistor to the calculated
value. With RFB1 calculate:
RFB2 =
V
FB(REG)
• R
FB1
VFLOAT – VFB(REG)
– 1000Ω
Figure6. Programming the Float Voltage with the LTC4120
22µF
RFB1
VFLOAT
Li-Ion
4120 F06
RFB2
ENABLE
BAT
FB
FBG
IFB
LTC4120
LTC4120/LTC4120-4.2
15
Rev. G
For more information www.analog.com
OPERATION
where 1000Ω represent the typical value of RFBG. This is
the resistance of the FBG pin which serves as the ground
return for the battery float voltage divider.
Once RFB1 and RFB2 are selected, recalculate the value of
VFLOAT obtained with the resistors available. If the error
is too large substitute another standard resistor value for
RFB1 and recalculate RFB2. Repeat until the float voltage
error is acceptable.
Table1 and Table2 list recommended standard 0.1% and
1% resistor values for common battery float voltages.
Table1. Recommended 0.1% Resistors for Common VFLOAT
VFLOAT RFB1 RFB2 TYPICAL ERROR
3.6V 887k 1780k –0.13%
4.1V 1.01M 1.42M 0.15%
4.2V 1.01M 1.35M –0.13%
7.2V 1.8M 898k 0.08%
8.2V 2.00M 825k 0.14%
8.4V 2.05M 816k 0.27%
Table2. Recommended 1% Resistors for Common VFLOAT
VFLOAT RFB1 RFB2 TYPICAL ERROR
3.6V 887k 1780k –0.13%
4.1V 1.02M 1.43M 0.26%
4.2V 1.02M 1.37M –0.34%
7.2V 1.78M 887k 0.16%
8.2V 2.00M 825k 0.14%
8.4V 2.1M 845k –0.50%
Programming the Charge Current
The current-error amp (C-EA) measures the current
through an internal 0.3Ω current sense resistor between
the CHGSNS and BAT pins. The C-EA outputs a fraction
of the charge current, 1/hPROG, to the PROG pin. The
voltage-error amp (V-EA) and PWM control circuitry can
limit the PROG pin voltage to control charge current. An
internal clamp (DZ) limits the PROG pin voltage to VPROG,
which in turn limits the charge current to:
ICHG =hPROG • VPROG
RPROG
=1212V
RPROG
ICHG_ TRKL =hPROG • VPROG_ TRKL
R
PROG
=120V
R
PROG
where hPROG is typically 988, VPROG is either 1.227V or
122mV during trickle charge, and RPROG is the resistance
of the grounded resistor applied to the PROG pin. The
PROG resistor sets the maximum charge current, or the
current delivered while the charger is operating in con-
stant-current (CC) mode.
Analog Charge Current Monitor
The PROG pin provides a voltage signal proportional to
the actual charge current. Care must be exercised in mea
-
suring this voltage as any capacitance at the PROG pin
forms a pole that may cause loop instability. If observing
the PROG pin voltage, add a series resistor of at least 2k
and limit stray capacitance at this node to less than 50pF.
In the event that the input voltage cannot support the
demanded charge current, the PROG pin voltage may
not represent the actual charge current. In cases such
as this, the PWM switch frequency drops as the charger
enters drop-out operation where the top switch remains
on for more than one clock cycle as the inductor current
attempts to ramp up to the desired current. If the top
switch remains on in drop-out for 8 clock cycles a dropout
detector forces the bottom switch on for the remainder
of the 8th cycle. In such a case, the PROG pin voltage
remains at 1.227V, but the charge current may not reach
the desired level.
Undervoltage Current Limit
The undervoltage current limit (UVCL) feature reduces
charge current as the input voltage drops below V
UVCL
LTC4120/LTC4120-4.2
16
Rev. G
For more information www.analog.com
OPERATION
(typically 12V). This low gain amplifier typically keeps VIN
within 100mV of VUVCL, but if insufficient power is avail-
able the input voltage may drop below this value; and the
charge current will be reduced to zero.
NTC Thermal Battery Protection
The LTC4120 monitors battery temperature using a therm-
istor during the charging cycle. If the battery temperature
moves outside a safe charging range, the IC suspends
charging and signals a fault condition until the tempera-
ture returns to the safe charging range. The safe charging
range is determined by two comparators that monitor the
voltage at the NTC pin. NTC qualified charging is disabled
if the NTC pin is pulled below about 85mV (VDIS).
Thermistor manufacturers usually include either a tem-
perature lookup table identified with a characteristic curve
number, or a formula relating temperature to the resistor
value. Each thermistor is also typically designated by a
thermistor gain value B25/85.
The NTC pin should be connected to a voltage divider
from INTVCC to GND as shown in Figure7. In the sim-
ple application (RADJ = 0) a 1% resistor, RBIAS, with a
value equal to the resistance of the thermistor at 25°C is
connected from INTVCC to NTC, and a thermistor is con-
nected from NTC to GND. With this setup, the LTC4120
pauses charging when the resistance of the thermistor
increases to 285% of the RBIAS resistor as the tempera-
ture drops. For a Vishay Curve 2 thermistor with B25/85
= 3490 and 25°C resistance of 10k, this corresponds to
a temperature of about 0°C. The LTC4120 also pauses
charging if the thermistor resistance decreases to 57.5%
of the RBIAS resistor. For the same Vishay Curve 2 therm-
istor, this corresponds to approximately 40°C. With a
Vishay Curve2 thermistor, the hot and cold comparators
both have about 2°C of hysteresis to prevent oscillations
about the trip points.
The hot and cold trip points may be adjusted using a dif-
ferent type of thermistor, or a different RBIAS resistor, or by
adding a desensitizing resistor, R
ADJ
, or by a combination
of these measures as shown in Figure7. For example, by
increasing RBIAS to 12.4k, with the same thermistor as
before, the cold trip point moves down to –5°C, and the
hot trip point moves down to 34°C. If a Vishay Curve 1
thermistor with B25/85 = 3950 and resistance of 100k at
25°C is used, a 1% RBIAS resistor of 118k and a 1% RADJ
resistor of 12.1k results in a cold trip point of 0°C, and a
hot trip point of 39°C.
End-Of-Charge Indication and Safety Timeout
The LTC4120 uses a safety timer to terminate charging.
Whenever the LTC4120 is in constant current mode the
timer is paused, and if FB transitions through the VRCHG
threshold the timer is reset. When the battery voltage
reaches the float voltage, a safety timer begins count-
ing down a 2-hour timeout. If charge current falls below
one-tenth of the programmed maximum charge current
(h
C/10
), the CHRG status pin rises, but top-off charge cur-
rent continues to flow until the timer finishes. After the
timeout, the LTC4120 enters a low power sleep mode.
Automatic Recharge
In sleep mode, the IC continues to monitor battery volt-
age. If the battery falls 2.2% (V
RCHG
or V
RCHG_42
) from the
Figure7. NTC Connections
+
RBIAS
RNTC Li-Ion
T
4120 F07
RADJ
OPT
BAT
NTC
74% INTVCC
TOO COLD
TOO HOT
IGNORE NTC
INTVCC
LTC4120
36.5% INTVCC
2% INTVCC
+
–
+
–
+
–
LTC4120/LTC4120-4.2
17
Rev. G
For more information www.analog.com
OPERATION
full-charge float voltage, the LTC4120 engages an auto-
matic recharge cycle. Automatic recharge has a built-in
filter of about 0.5ms to prevent triggering a new charge
cycle if a load transient causes the battery voltage to
droptemporarily.
State of Charge and Fault Status Pins
The LTC4120 contains two open-drain outputs which
provide charge status and signal fault indications. The
binary-coded CHRG pin pulls low to indicate charging at a
rate higher than C/10. The FAULT pin pulls low to indicate
a bad battery timeout, or to indicate an NTC thermal fault
condition. During NTC faults the CHRG pin remains low,
but when a bad battery timeout occurs the CHRG pin de-
asserts. When the open-drain outputs are pulled up with
a resistor, Table3 summarizes the charger state that is
indicated by the pin voltages.
Table3. LTC4120 Open-Drain Indicator Outputs with Resistor
Pull-Ups
FAULT CHRG CHARGER STATE
High High Off or Topping Off Charging at a Rate Less Than C/10
High Low Charging at Rate Higher Than C/10
Low High Bad Battery Fault
Low Low NTC Thermal Fault Charging Paused
Low Battery Voltage Operation
The LTC4120 automatically preconditions heavily dis-
charged batteries. If the battery voltage is below V
LOWBAT
minus its hysteresis (typically 2.05V—e.g., battery pack
protection has been engaged) a DC current, ILOWBAT, is
applied to the BAT pin from the INTVCC supply. When the
battery voltage rises above V
LOWBAT
, the switching regula-
tor is enabled and charges the battery at a trickle charge
level of 10% of the full-scale charge current (in addition
to the DC ILOWBAT current). Trickle charging of the battery
continues until the sensed battery voltage (sensed via
the feedback pin for the LTC4120) rises above the trickle
charge threshold, V
TRKL
. When the battery rises above
the trickle charge threshold, the full-scale charge current
is applied and the DC trickle charge current is turned off.
If the battery remains below the trickle charge thresh-
old for more than 30 minutes, charging terminates and
the fault status pin is asserted to indicate a bad battery.
After a bad battery fault, the LTC4120 automatically
restarts a new charge cycle once the failed battery is
removed and replaced with another battery. The LTC4120-
4.2 monitors the BATSNS pin voltage to sense LOWBAT
and TRKL conditions.
Precision Run/Shutdown Control
The LTC4120 remains in a low power disabled mode until
the RUN pin is driven above VEN (typically 2.45V). While
the LTC4120 is in disabled mode, current drain from the
battery is reduced to extend battery lifetime, the status
pins are both de-asserted, and the FBG pin is high imped-
ance. Charging can be stopped at any time by pulling
the RUN pin below 2.25V. The LTC4120 also offers an
extremely low operating current shutdown mode when
the RUN pin is pulled below VSD (typically 0.7V). In this
condition less than 20µA is drawn from the supply at IN.
Differential Undervoltage Lockout
The LTC4120 monitors the difference between the bat-
tery voltage, VBAT, and the input supply, VIN. If the differ-
ence (VIN-VBAT) falls to VDUVLO, all functions are disabled
and the part is forced into shutdown mode until (VIN-
VBAT) rises above the VDUVLO hysteresis. The LTC4120-
4.2 monitors the BATSNS and IN pin voltages to sense
DUVLO condition.
User Selectable Buck Operating Frequency
The LTC4120 uses a constant-frequency synchronous
step-down buck architecture to produce high operat-
ing efficiency. The nominal operating frequency of the
buck, f
OSC
, is programmed by connecting the FREQ pin to
either INTVCC or to GND to obtain a switching frequency
of 1.5MHz or 750kHz, respectively. The high operating
frequency allows the use of smaller external components.
Selection of the operating frequency is a trade-off between
efficiency, component size, and margin from the minimum
on-time of the switcher. Operation at lower frequency
LTC4120/LTC4120-4.2
18
Rev. G
For more information www.analog.com
OPERATION
improves efficiency by reducing internal gate charge and
switching losses, but requires larger inductance values to
maintain low output ripple. Operation at higher frequency
allows the use of smaller components, but may require
sufficient margin from the minimum on-time at the lowest
duty cycle if fixed-frequency switching is required.
PWM Dropout Detector
If the input voltage approaches the battery voltage, the
LTC4120 may require duty cycles approaching 100%.
This mode of operation is known as dropout. In drop-
out, the operating frequency may fall well below the pro-
grammed fOSC value. If the top switch remains on for eight
clock cycles, the dropout detector activates and forces the
bottom switch on for the remainder of that clock cycle
or until the inductor current decays to zero. This avoids
a potential source of audible noise when using ceramic
input or output capacitors and prevents the boost sup-
ply capacitor for the top gate drive from discharging. In
dropout operation, the actual charge current may not be
able to reach the full-scale programmed value. In such a
scenario the analog charge current monitor function does
not represent actual charge current being delivered.
Burst Mode Operation
At low charge currents, for example during constant-
voltage mode, the LTC4120 automatically enters Burst
Mode operation. In Burst Mode operation the switcher is
periodically forced into standby mode in order to improve
efficiency. The LTC4120 automatically enters Burst Mode
operation after it exits constant-current (CC) mode and
as the charge current drops below about 80mA. Burst
Mode operation is triggered at lower currents for larger
PROG resistors, and depends on the input supply volt-
age. Refer to graph Burst Mode Trigger Current and graph
Typical Burst Mode Waveform, in the Typical Performance
Characteristics, for more information on Burst Mode
operation. Burst Mode operation has some hysteresis and
remains engaged for battery currents up to about 150mA.
While in Burst Mode operation, the PROG pin voltage to
average charge current relationship is not well defined.
This is due to the PROG pin voltage falling to 0V in
between bursts, as shown in G14. If the PROG pin volt-
age falls below 120mV for longer than 350µs this causes
the CHRG pin to de-assert, indicating C/10. Burst current
ripple depends on the selected switch inductor, and VIN/
VBAT.
BOOST Supply Refresh
The BOOST supply for the top gate drive in the LTC4120
switching regulator is generated by bootstrapping the
BOOST flying capacitor to INTVCC whenever the bottom
switch is turned on. This technique provides a voltage of
INTVCC from the BOOST pin to the SW pin. In the event
that the bottom switch remains off for a prolonged period
of time, e.g., during Burst Mode operation, the BOOST
supply may require a refresh. Similar to the PWM dropout
timer, the LTC4120 counts the number of clock cycles
since the last BOOST refresh. When this count reaches
32, the next PWM cycle begins by turning on the bottom
side switch first. This pulse refreshes the BOOST flying
capacitor to INTV
CC
and ensures that the topside gate
driver has sufficient voltage to turn on the topside switch
at the beginning of the next cycle.
Operation Without an Input Supply or Wireless Power
When a battery is the only available power source, care
should be taken to eliminate loading of the IN pin. Load
current on IN drains the battery through the body diode
of the top side power switch as VIN falls below VSW. To
prevent this possibility, place a diode between the input
supply and the IN capacitor, CIN. The rectification diode
(D9 in Figure5 and Figure11) in the wireless power appli-
cations also eliminates this discharge path. Alternately, a
P-channel MOSFET may be placed in series with the BAT
pin provided care is taken to directly sense the positive
battery terminal voltage with FB via the battery resistive
divider. This is illustrated in Figure15.
LTC4120/LTC4120-4.2
19
Rev. G
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APPLICATIONS INFORMATION
Wireless Power Transfer
In a wireless power transfer system, power is transmitted
using alternating magnetic fields. Power is transferred
based on the principle that an AC current in a transmit-
ter coil produces an AC current in a receiver coil that is
placed in the magnetic field generated by the transmit-
ter coil. The magnetic field coupling is described by the
mutual inductance, M. This term does not have a physical
representation but is referred to using the unit-less terms
k and n. Where k is the coupling coefficient:
k=M
L
X
• L
R
And n is the turns ratio—the number of turns in the receiver
coil divided by the number of turns in the transmitter coil:
n=nR
nX
=LR
LX
The turns ratio is proportional to the square root of the
ratio of receiver coil inductance to transmitter coil induc-
tance. In the wireless power transfer system an AC cur-
rent, IAC, applied to the transmit coil LX, produces an AC
current in the receive coil, LR of:
IR(AC) = 2 • π • M • IAC = 2 • π • k • √LX • LR • IAC
The coupling coefficient is a variable that depends on the
orientation and proximity of the transmitter coil relative
to the receiver coil. If the two coils are in a transformer,
then k = 1. If the two coils are completely isolated from
each other then k = 0. In a typical LTC4120-based wireless
power design, k varies from around 0.18 at 10mm spac-
ing, to about 0.37 with the coils at 3mm spacing. This is
illustrated in Figure9.
With low resistance in the LX and LR coils, the efficiency
is inherently high, even at low coupling ratios. The trans-
mitter in Figures 4 and 10 generates a sine wave at the
resonant frequency, fO, across the transmitter coil and
capacitor (LX||CX). With a peak-to-peak amplitude that is
proportional to the applied input voltage:
VAC ≅ 2 • π • VDC
This generates a sinusoidal current in the transmit coil
with peak-to-peak amplitude:
IAC =
V
AC
2 • π• fO• LX
≅
V
DC
fO• LX
The AC voltage induced at the receive coil is a function
of both the applied voltage, the coupling, as well as the
impedance at the receiver. With no load at the receiver, the
open-circuit voltage, VIN(OC), is approximately:
VIN(OC) ≅ k • n • 2 • π • VDC
The receiver (shown in Figures 5 and 10) uses a resonant
tuned circuit followed by a rectifier to convert the induced
AC voltage into a DC voltage to power the LTC4120 and
charge a battery. Power delivered to the LTC4120 depends
on the impedance of the LTC4120 and the impedance of
the tuned circuit at the resonant frequency of the trans-
mitter. The LTC4120 employs a proprietary circuit, called
dynamic harmonization control (DHC) that modulates the
impedance of the receiver depending on the voltage at the
input to the LTC4120. This technique ensures that over a
wide range of coupling coefficients the induced rectified
voltage does not exceed voltage compliance ratings when
the load goes away (e.g, when the battery is fully charged).
DHC efficiently adjusts the receiver impedance depending
on the load without compromising availablepower.
In the event that the coupling may become too large (e.g.
receiver coil is placed too close to the transmitter coil)
then it is recommended to place a Zener diode across the
Figure9. Coupling Coefficient k vs Distance
+
++
+
+
++
X
X
X
X
X
X
X
X
X
X
X
X
XX
0.50
NO MISALIGNMENT
5mm MISALIGNMENT
10mm MISALIGNMENT
0.45
0.40
0.35
0.30
COUPLING COEFFICIENT (k)
0.25
0.20
0.15
0.10 012345
COIL DISTANCE (mm)
6 7 8 9 10
4120 F09
Figure8. Wireless Power Transfer
IR
1:n
I
AC
LR
4120 F08
LXV
R
LTC4120/LTC4120-4.2
20
Rev. G
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APPLICATIONS INFORMATION
input to the LTC4120 to prevent exceeding the absolute
maximum rating of the LTC4120. Diode D6 (in Figure4
and Figure10) illustrates this connection.
The RMS voltage at the rectifier output depends on the
load of the LTC4120, i.e., the charge current, as well as the
applied AC current, IAC. The applied AC current depends
both on the components of the tuned network as well as
the applied DC voltage. The load at the receiver depends
on the state of charge of the battery. If the coupling and/or
the applied AC current is not well controlled, the addition
of a 39V Zener diode (D6 in Figures 4 and 10) at the input
to the LTC4120 will prevent overvoltage conditions from
damaging the LTC4120.
Resonant Transmitter and Receiver
An example DC/AC transmitter is shown in Figure10.
A 5V ±5% supply to the transmitter efficiently produces a
circulating AC current in LX, which is coupled to LR. For
higher voltage inputs, a pre-regulator DC/DC converter
can be used to generate 5V (see Figure11). Power is
transmitted from transmitter to receiver at the resonant
C4
0.01µF
R1
100Ω
C5
0.01µF
CX
0.3µF LX
5µH LRD2
D1
LB1
68µH LB2
68µH
VCC
4.75V TO 5.25V TRANSMITTER RECEIVER
R2
100Ω
D2
M1 M2
D3
D1 D4
D3
C3
L1
C2S2
C2S1
C2P1
C1
10µF
C5
10µF
D4
39V
OPT
C4
2.2µF C2
47µF
C2P2
DHC
INTVCC
BOOST
SW
CHGSNS
BAT
FB
FBG
4120 F10
IN
GND
U1
LTC4120
+
VIN
U1
LT3480
GND
BD
BOOST
SW
PG
VC
RUN/SS
SYNC
RT
FB
C9
0.47µF
C7
0.068µF
C8
330pF
R5
20k
C10
22µF
M4
2N7002L
M3
Si2333DS
VCC
5V
CONNECT
TO Tx VCC
R8
150k
L3
4.7µF
D5
DFLS240L
C6
4.7µF
HVIN
8V TO 38V
GND
R4
40.2k
R3
150k
R7
536k
R10
100k
R6
100k
4120 F11
Figure10. DC/AC Converter, Transmit/Receive Coils, Tuned Series Resonant Receiver and AC/DC Rectifier
Figure11. High Voltage Pre-Regulator for Transmitter
LTC4120/LTC4120-4.2
21
Rev. G
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APPLICATIONS INFORMATION
Table4. Recommended Transmitter and High Voltage Pre-Regulator Components
Transmitter Components
ITEM DESCRIPTION MANUFACTURER/PART NUMBER
D2, D3 DIODE, SCHOTTKY, 40V, 2A ON SEMI NSR10F40NXT5G
D1, D4 DIODE, ZENER, 16V, 350mW, SOT23 DIODES BZX84C16
M1, M2 MOSFET, SMT, N-CHANNEL, 60V, 11mΩ, S08 VISHAY Si4470EY-T1GE3
LB1, LB2 IND, SMT, 68µH, 0.41A, 0.4Ω, ±20% TDK VLCF5028T-680MR40-2
C4, C5 CAP, CHIP, X7R, 0.01µF, ±10%, 50V, 0402 MURATA GRM155R71H103KA88D
R1, R2 RES, CHIP, 100Ω, ±5%, 1/16W, 0402 VISHAY CRCW0402100RJNED
CX1, 2 CAP, CHIP, PPS, 0.15µF, ±2%, 50V PANASONIC ECHU1H154GX9
CAP, CHIP, PPS, 0.1µF, ±2%, 50V PANASONIC ECHU1H104GX9
CAP, CHIP, PPS, 0.033µF, ±2%, 50V PANASONIC ECHU1H333GX9
CX (Opt) CAP, PPS, 0.15µF, ±2.5%, 63VAC, MKS02 WIMA MKS0D031500D00JSSD
CAP, PPS, 0.10µF, ±2.5%, 63VAC, MKS02 WIMA MKS0D03100
CAP, PPS, 0.033µF, ±2.5%, 63VAC, MKS02 WIMA MKS0D03033
LX5.0µH TRANSMIT COIL TDK WT-505060-8K2- LT
or 6.3µH TRANSMIT COIL TDK WT-505090-10K2-A11-G
or 6.3µH TRANSMIT COIL WÜRTH 760308111
or 5.0µH TRANSMIT COIL INTER-TECHNICAL L41200T02
High Voltage Pre-Regulator Components
U1 LT3480EDD, PMIC 38V, 2A, 2.4MHz Step-Down Switching
Regulator with 70µA Quiescent Current LINEAR TECH LT3480EDD
M3 MOSFET, SMT, P-CHANNEL, –12V, 32mΩ, SOT23 VISHAY Si2333DS
M4 MOSFET, SMT, N-CHANNEL, 60V, 7.5Ω, 115mA, SOT23 ON SEMI 2N7002L
D5 DIODE, SCHOTTKY, 40V, 2A, POWERDI123 DIODES DFLS240L
L3 IND, SMT, 4.7µH, 1.6A, 0.125Ω, ±20% COILCRAFT LPS4018-472M
C6 CAP, CHIP, X5R, 4.7µF, ±10%, 50V, 1206 MURATA GRM155R71H4755KA12L
C7 CAP, CHIP, X5R, 4.7µF, ±10%, 50V, 0603 MURATA GRM188R71H683K
C8 CAP, CHIP, COG, 330pF, ±5%, 50V, 0402 TDK C1005COG1H331J
C9 CAP, CHIP, X7R, 0.47µF, ±10%, 25V, 0603 MURATA GRM188R71E474K
C10 CAP, CHIP, X5R, 22µF, ±20%, 6.3V, 0805 TAIYO-YUDEN JMK212BJ226MG
R3, R8 RES, CHIP, 150k, ±5%, 1/16W, 0402 VISHAY CRCW0402150JNED
R4 RES, CHIP, 40.2k, ±1%, 1/16W, 0402 VISHAY CRCW040240K2FKED
R5 RES, CHIP, 20k, ±1%, 1/16W, 0402 VISHAY CRCW040220K0FKED
R6, R10 RES, CHIP, 100k, ±1%, 1/16W, 0402 VISHAY CRCW0402100KFKED
R7 RES, CHIP, 536k, ±1%, 1/16W, 0402 VISHAY CRCW0402536KFKED
1CX = 300nF with 5µH LX coil, or CX = 233nF with 6.3µH LX coil.
2Pay careful attention to assembly guidelines when using ECHU capacitors, as the capacitance value may shift if the capacitor is over heated while
soldering. Plastic film capacitors such as Panasonic ECHU series or Metallized Polypropylene capacitors such as WIMA MKP as suitable for the transmitter
frequency, fO; which depends on both component values
as well as the load at the receiver. The tolerance of the
components selected in both the transmitter and receiver
circuits is critical to achieving maximum power transfer.
The voltages across the receiver components may reach
40V, so adequate voltage ratings must also be observed.
Resonant Converter Component Selection
It is recommended to use the components listed in Table4
and Table5 for the resonant transmitter and receiver
respectively. Figure12 illustrates the PCB layout of the
embedded receiver coil. Figure13 and Figure14 show the
finished transmitter and receiver. The 25mm ferrite bead
LTC4120/LTC4120-4.2
22
Rev. G
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APPLICATIONS INFORMATION
Table5. Recommended Receiver Components
ITEM DESCRIPTION MANUFACTURER/PART NUMBER
D1, D2, D3 DIODE, SCHOTTKY, 40V, 2A, POWERDI123 DIODES DFLS240L
D4 (Opt) DIODE, ZENER, 39V, ±5%, 1W, POWERDI123 DIODES DFLZ39
LRIND, EMBEDDED, 47µH, 43 TURNS WITH 25mm FERRITE BEAD EMBEDDED 4-LAYER PCB (see Figure12)
ADAMS MAGNETICS B67410-A0223-X195
or 47µH RECEIVER COIL TDK WR282840-37K2-LR3
or 47µH RECEIVER COIL WÜRTH 760308101303
or 48µH RECEIVER COIL INTER-TECHNICAL L41200R02
L1 IND, SMT, 15µH, 260mΩ, ±20%, 0.86A, 4mm × 4mm COILCRAFT LPS4018-153ML
C2P1 CAP, CHIP, COG, 0.0047µF, ±5%, 50V, 0805 MURATA GRM21B5C1H472JA01L
C2P2 CAP, CHIP, COG, 0.00018µF, ±5%, 50V, 0603 KEMET C0603C182J5GAC7533
C2S1 CAP, CHIP, COG, 0.022µF, ±5%, 50V, 0805 MURATA GRM21B5C1H223JA01L
C2S2 CAP, CHIP, COG, 0.0047µF, ±5%, 50V, 0805 MURATA GRM21B5C1H472JA01L
C1 CAP, CHIP, X5R, 10µF, ±20%, 16V, 0805 TDK C2012X5R1C106K
C2 CAP, CHIP, X5R, 47µF, ±10%, 16V, 1210 MURATA GRM32ER61C476KE15L
C3 CAP, CHIP, X7R, 0.01µF, ±20%, 6.3V. 0402 TDK C1608X7R1H103K
C4 CAP, CHIP, X5R, 10µF, ±20%, 16V, 0805 TDK C2012X5R1C106K
U1 400mA WIRELESS SYNCHRONOUS BUCK BATTERY CHARGER LINEAR TECH LTC4120
TOP METAL
3rd METAL
2nd METAL
BOTTOM METAL
4120 F12
L1 – TOP SIDE
L2
L3
L4 – BOTTOM SIDE
FINISHED THICKNESS TO BE 0.031" ±0.005"
TOTAL OF 4 LAYERS WITH 2oz CU ON THE
OUTER LAYERS AND 2oz CU ON THE INNER
LAYERS
LAYER STRUCTURE
Figure12. 4-Layer PCB Layout of Rx Coil
LTC4120/LTC4120-4.2
23
Rev. G
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APPLICATIONS INFORMATION
in Figure14 covers the embedded receiver coil described
in Figure12. Gerber layout files for both the transmitter
and receiver boards are available at the following link:
LTC4120 Evaluation Kits
Alternative component values can be chosen by following
the design procedure outlined below.
Resonant Transmitter Tuning: LX, CX
The basic transmitter (shown in Figure4) has a resonant
frequency, fO, that is determined by components LX, and
CX. The selection of LX and CX are coupled so as to obtain
the correct operating frequency. The selection of LX and
LR is also coupled to ideally obtain a turns ratio of 1:3.
Having selected a transmitter inductor, LX, the transmitter
capacitor should be selected to obtain a resonant
frequency of 130kHz. Due to limited selection of standard
values, several standard value capacitors may need to be
used in parallel to obtain the correct value for fO:
fO≅
1
2 • π• LX• CX
=130kHz
The transmitter inductor and capacitor, LX and CX, sup-
port a large circulating current. Series resistance in the
inductor is a source of loss and should be kept to a
minimum for optimal efficiency. Likewise the transmitter
capacitor(s), CX, must support large ripple currents and
must be selected with adequate voltage rating and low
dissipation factors.
Resonant Receiver Tuning: LR, C2S, C2P
The tuned circuit resonance of the receiver, fT, is determined
by the selection of LR and C2S + C2P. Select the capacitors
to obtain a resonant frequency 1% to 3% below fO:
fT≅1
2 • π• LR• C2P +C2S
( )
As in the case of the transmitter, multiple parallel capaci-
tors may need to be used to obtain the optimum value.
Finally, select the detuned resonance, fD to be about 5%
to 15% higher than the tuned resonance, keeping the
value of C2P below 30nF to limit power dissipation in
the DHCpin:
fD≅
1
2 • π• LR• C2S
Alternative Transmitter Options
The resonant DC/AC transmitter discussed in the
previous section is a basic and inexpensive to build
transmitter. However, this basic transmitter requires a
relatively precise DC input voltage to meet a given set
of receive power requirements. It is unable to prevent
power transmission to foreign metal objects—and can
therefore cause these objects to heat up. Furthermore,
Figure13. Tx Layout: Demo Circuit 1968A
Figure14. Rx Layout with Ferrite Shield: Demo Circuit 1967A-B
LTC4120/LTC4120-4.2
24
Rev. G
For more information www.analog.com
APPLICATIONS INFORMATION
the operating frequency of the basic transmitter can vary
with componentselection.
LTC4120 customers can also choose more advanced
transmitter options such as the LTC4125. With addi-
tional features such as: foreign metal detection; optimum
power search and AutoResonant™ operating frequency.
For more information on advanced transmitter options
refer to the Wireless Power Users Guide.
Maximum Battery Power Considerations
Using one of the approved transmitter options with this
wireless power design provides a maximum of 2W at the
input to the LTC4120. It is optimized for supplying 400mA
of charge current to a 4.2V Li-Ion battery. If a higher bat-
tery voltage is selected, then a lower charge current must
be used as the maximum power available is limited. The
maximum battery charge current, ICHG(MAX), that may be
programmed for a given float voltage, VFLOAT, can be cal-
culated based on the charger efficiency, ηEFF, as:
ICHG(MAX) ≤ηEFF
• 2W
VFLOAT
The charger efficiency, η
EFF
, depends on the operating
conditions and may be estimated using the Buck Efficiency
curve in the Typical Performance Characteristics. Do not
select a charge current greater than this limit when select-
ing RPROG.
Input Voltage and Minimum On-Time
The LTC4120 can operate from input voltages up to 40V.
The LTC4120 maintains constant frequency operation
under most operating conditions. Under certain situa-
tions with high input voltage and high switching frequency
selected and a low battery voltage, the LTC4120 may not
be able to maintain constant frequency operation. These
factors, combined with the minimum on-time of the
LTC4120, impose a minimum limit on the duty cycle to
maintain fixed-frequency operation. The on-time of the
top switch is related to the duty cycle (VBAT/VIN) and the
switching frequency, fOSC in Hz:
tON =
V
BAT
fOSC • VIN
When operating from a high input voltage with a low bat-
tery voltage, the PWM control algorithm may attempt
to enforce a duty cycle which requires an on-time lower
than the LTC4120 minimum, tMIN(ON). This minimum
duty cycle is approximately 18% for 1.5MHz operation
or 9% for 750kHz operation. Typical minimum on-time
is illustrated in graph G11 in the Typical Performance
Characteristics section. If the on-time is driven below
tMIN(ON), the charge current and battery voltage remain
in regulation, but the switching duty cycle may not remain
fixed, and/or the switching frequency may decrease to an
integer fraction of its programmed value.
The maximum input voltage allowed to maintain constant
frequency operation is:
VIN(MAX) =
V
LOWBAT
fOSC • tMIN(ON)
where VLOWBAT, is the lowest battery voltage where the
switcher is enabled.
Exceeding the minimum on-time constraint does not
affect charge current or battery float voltage, so it may not
be of critical importance in most cases and high switch-
ing frequencies may be used in the design without any
fear of severe consequences. As the sections on Inductor
Selection and Capacitor Selection show, high switching
frequencies allow the use of smaller board components,
thus reducing the footprint of the applications circuit.
Fixed-frequency operation may also be influenced by drop-
out and Burst Mode operation as discussed previously.
Switching Inductor Selection: LSW
The primary criterion for switching inductor value selec-
tion in an LTC4120 charger is the ripple current created in
that inductor. Once the inductance value is determined, the
saturation current rating for that inductor must be equal
to or exceed the maximum peak current in the inductor,
IL(PEAK). The peak value of the inductor current is the sum
of the programmed charge current, ICHG, plus one-half of
the ripple current, ∆IL. The peak inductor current must
also remain below the current limit of the LTC4120, IPEAK:
IL(PEAK) =ICHG +∆
I
L
2
<IPEAK
LTC4120/LTC4120-4.2
25
Rev. G
For more information www.analog.com
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The current limit of the LTC4120, I
PEAK
, is at least 585mA
(and at most 1250mA). The typical value of IPEAK is
illustrated in graph RSNS Current Limit vs Temperature,
in the Typical Performance Characteristics.
For a given input and battery voltage, the inductor value
and switching frequency determines the peak-to-peak rip-
ple current amplitude according to the following formula:
∆IL=VIN – VBAT
( )
• VBAT
fOSC • VIN • LSW
Ripple current is typically set to be within a range of 20%
to 40% of the programmed charge current, ICHG. To obtain
a ripple current in this range, select an inductor value
using the nearest standard inductance value available that
obeys the following formula:
LSW ≥VIN(MAX) – VFLOAT
( )
• VFLOAT
fOSC • VIN(MAX) • 30% •ICHG
( )
Then select an inductor with a saturation current rating at
a value greater than IL(PEAK).
Input Capacitor: CIN
The LTC4120 charger is biased directly from the input
supply at the V
IN
pin. This supply provides large switched
currents, so a high quality, low ESR decoupling capaci-
tor is recommended to minimize voltage glitches at VIN.
Bulk capacitance is a function of the desired input ripple
voltage (∆VIN), and follows the relation:
CIN(BULK) =
ICHG
V
BAT
VIN
∆VIN
µF
( )
Input ripple voltages (∆VIN) above 10mV are not recom-
mended. 10µF is typically adequate for most charger
applications, with a voltage rating of 40V.
Reverse Blocking
When a fully charged battery is suddenly applied to the
BAT pin, a large in-rush current charges the C
IN
capaci-
tor through the body diode of the LTC4120 topside power
switch. While the amplitude of this current can exceed sev-
eral Amps, the LTC4120 will survive provided the battery
voltage is below the maximum value of 11V. To completely
eliminate this current, a blocking P-channel MOSFET can be
placed in series with the BAT pin. When the battery is the
only source of power, this PFET also serves to decrease bat-
tery drain current due to any load placed at VIN. As shown
in Figure15, the PFET body diode serves as the blocking
component since CHRG is high impedance when the bat-
tery voltage is greater than the input voltage. When CHRG
pulls low, i.e. during most of a normal charge cycle, the
PFET is on to reduce power dissipation. This PFET requires
a forward current rating equal to the programmed charge
current and a reverse breakdown voltage equal to the pro-
grammed float voltage. Figure15 illustrates how to add a
blocking PFET connected with the LTC4120.
APPLICATIONS INFORMATION
Figure15. Reverse Blocking with a P-Channel MOSFET in Series with the BAT Pin
+
BAT
BST
SW
CHGSNS
22µF
10µF 22nF
2.2µF
RPROG
RFB1
49.9k
4.99k*
470k
RFB2
Li-Ion
FB
FBG
GND
CHRG
RUN
INTVCC
VIN
VIN
LTC4120
SI2343DS
PROG
4.7µF
LSW
4120 F15
*ADD 4.99k WHEN MAX BAT VOLTAGE APPROACHES 85% OF VGS LIMIT FOR Si2343.
LTC4120/LTC4120-4.2
26
Rev. G
For more information www.analog.com
APPLICATIONS INFORMATION
BAT Capacitor and Output Ripple: CB AT
The LTC4120 charger output requires bypass capaci-
tance connected from BAT to GND (C
BAT
). A 22µF ceramic
capacitor is required for all applications. In systems where
the battery can be disconnected from the charger out-
put, additional bypass capacitance may be desired. In this
type of application, excessive ripple and/or low ampli-
tude oscillations can occur without additional output bulk
capacitance. For optimum stability, the additional bulk
capacitance should also have a small amount of ESR. For
these applications, place a 100µF low ESR non-ceramic
capacitor (chip tantalum or organic semiconductor capac-
itors such as Sanyo OS-CONs or POSCAPs) from BAT to
GND, in parallel with the 22µF ceramic bypass capacitor,
or use large ceramic capacitors with an additional series
ESR resistor of less than 1Ω. This additional bypass
capacitance may also be required in systems where the
battery is connected to the charger with long wires. The
voltage rating of all capacitors applied to CBAT must meet
or exceed the battery float voltage.
Boost Supply Capacitor: CBST
The BOOST pin provides a bootstrapped supply rail that
provides power to the top gate drivers. The operating volt-
age of the BOOST pin is internally generated from INTVCC
whenever the SW pin pulls low. This provides a floating
voltage of INTV
CC
above SW that is held by a capacitor tied
from BOOST to SW. A low ESR ceramic capacitor of 10nF
to 22nF is sufficient for CBST, with a voltage rating of 6V.
INTVCC Supply and Capacitor: CINTVCC
Power for the top and bottom gate drivers and most other
internal circuitry is derived from the INTV
CC
pin. A low
ESR ceramic capacitor of 2.2µF is required on the INTVCC
pin. The INTVCC supply has a relatively low current limit
(about 20mA) that is dialed back when INTVCC is low to
reduce power dissipation. Do not use the INTVCC voltage
to supply power for any external circuitry apart from the
NTCBIAS network. When the RUN pin is above VEN the
INTVCC supply is enabled, and when INTVCC rises above
UVINTVCC the charger is enabled.
APPLICATIONS INFORMATION
Calculating Power Dissipation
The user should ensure that the maximum rated junction
temperature is not exceeded under all operating condi-
tions. The thermal resistance of the LTC4120 package
(θ
JA
) is 54°C/W; provided that the exposed pad is sol-
dered to sufficient PCB copper area. The actual thermal
resistance in the application may depend on forced air
cooling or other heat sinking means, and especially the
amount of copper on the PCB to which the LTC4120 is
attached. The actual power dissipation while charging is
approximated by the following formula:
PD≅VIN – VBAT
( )
•ITRKL
+VIN •IIN(SWITCHING)
+RSNS •ICHG2
+RDS(ON)(TOP) •VBAT
VIN
•ICHG2
+RDS(ON)(BOT) • 1– VBAT
VIN
⎛
⎝
⎜
⎞
⎠
⎟•ICHG2
During trickle charge (VBAT < VTRKL) the power dissipation
may be significant as I
TRKL
is typically 10mA, however
during normal charging the ITRKL term is zero.
The junction temperature can be estimated using the fol-
lowing formula:
TJ = TA + PD • θJA
where TA is the ambient operating temperature.
Significant power is also consumed in the transmitter
electronics. The large AC voltage generated across the
LX and CX tank results in power being dissipated in the DC
resistance of the LX coil and the ESR of the CX capacitor.
The large induced magnetic field in the LX coil may also
induce heating in nearby metallic objects.
PCB Layout
To prevent magnetic and electrical field radiation and
high frequency resonant problems, proper layout of the
components connected to the LTC4120 is essential. For
maximum efficiency, the switch node rise and fall times
LTC4120/LTC4120-4.2
27
Rev. G
For more information www.analog.com
APPLICATIONS INFORMATION
should be minimized. The following PCB design priority
list will help insure proper topology. Layout the PCB using
the guidelines listed below in this specific order.
1. Keep foreign metallic objects away from the transmit-
ter coil. Metallic objects in proximity to the transmit
coil will suffer from induction heating and will be a
source of power loss. With the exception of a ferrite
shield that can be used to improve the coupling from
transmitter coil to receiver coil when placed behind
the transmitter coil.
Advanced transmitters using LTC4125 include
features to detect the presence of foreign metallic
objects that mitigates this issue.
2. VIN input capacitor should be placed as close as pos-
sible to the IN and GND pins, with the shortest copper
traces possible and a via connection to the GND plane
3. Place the switching inductor as close as possible to the
SW pin. Minimize the surface area of the SW pin node.
Make the trace width the minimum needed to support
the programmed charge current, and ensure that the
spacing to other copper traces be maximized to reduce
capacitance from the SW node to any other node.
4. Place the BAT capacitor adjacent to the BAT pin and
ensure that the ground return feeds to the same cop-
per that connects to the input capacitor ground before
connecting back to system ground.
5. Route analog ground (RUN ground and INTVCC capac-
itor ground) as a separate trace back to the LTC4120
GND pin before connecting to any other ground.
6. Place the INTV
CC
capacitor as close as possible to the
INTVCC pin with a via connection to the GND plane.
7. Route the DHC trace with sufficient copper and vias
to support 350mA of RMS current, and ensure that
the spacing from the DHC node to other copper traces
be maximized to reduce capacitance and radiated EMI
from the DHC node to other sensitive nodes.
8. It is important to minimize parasitic capacitance on
the PROG pin. The trace connecting to this pin should
be as short as possible with extra wide spacing from
adjacent copper traces.
9. Minimize capacitive coupling to GND from the FB pin.
10. Maximize the copper area connected to the exposed
pad. Place via connections directly under the exposed
pad to connect a large copper ground plane to the
LTC4120 to improve heat transfer.
Design Examples
The design example illustrated in Figure17, reviews the
design of the resonant coupled power transfer charger
application. First the design of the wireless power receiver
circuit is described. Then consider the design for the char-
ger function given the maximum input voltage, a battery
float voltage of 8.2V, and a charge current of 200mA for
the LTC4120. This example also demonstrates how to
select the switching inductance value to avoid discontinu-
ous conduction; where switching noise increases.
The wireless power receiver is formed by the tuned net-
work LR and C2P, C2S. This tuned network automatically
modulates the resonance of the tank with the DHC pin of
the LTC4120 to optimize power transfer. The resonant
frequency of the tank should match the oscillation fre-
quency of the transmitter. Given the transmitter shown
in Figure4 this frequency is 130kHz. The tuned receiver
resonant frequency is:
fT=
1
2 • π• LR • (C2P +C2S) =127kHz
In this design example, the de-tuned resonant frequency
is:
fD=
1
2 • π• LR • C2S =142kHz
fD should be set between 5% and 15% higher than fT. A
higher level gives more control range but results in more
power dissipation.
A 47µH coil is selected for L
R
to obtain a turns ratio of 3:1
from the transmitter coil, LX = 5µH.
Now C2S can be calculated to be 26.7nF. Two standard
parallel 50V rated capacitors, 22nF and 4.7nF, provide
a value within 1% of the calculated C2S. Now C2P can
be calculated to be 6.5nF which can be obtained with
LTC4120/LTC4120-4.2
28
Rev. G
For more information www.analog.com
APPLICATIONS INFORMATION
4.7nF and 1.8nF capacitors in parallel. All of the capacitors
should be selected with 5% or better tolerance.
The rectifier, D8, D9 and D5 are selected as 50V rated
Schottky diodes.
Now consider the design circuit for the LTC4120 charger
function. First, the external feedback divider, RFB1/RFB2,
is found using standard 1% values:
RFB1 =
8.2V • 588k
2.4V ≅2.00M
RFB2 =2.00M • 588k
2.00M – 588k
≅825k
With these resistors, and including the resistance of the
FBG pin, the battery float voltage is 8.212V.
With an 8.2V float voltage the maximum charge current
available is limited by the maximum power available from
the RCPT at ηEFF = 85% charger efficiency:
ICHG(MAX) ≤
85% • 2W
8.2V
=207mA
A charge current of 200mA is achieved by selecting a
standard 1% RPROG resistor of:
RPROG =hPROG • VPROG
I
CHG
=6.04k
While charging a battery, the resonant receiver is loaded
by the charge current, this load reduces the input voltage
from the open-circuit value to a typical voltage in a range
from 12V (at UVCL) up to about 26V. The amplitude of
this voltage depends primarily on the amount of coupling
between the transmitter and the receiver, typically this
voltage is about 17V.
The maximum loaded input voltage is used to select
the operating frequency and influences the value of the
switching inductor. The saturation current rating of the
switching inductor is selected based on the worst case
conditions at the maximum open-circuit voltage.
A typical 2-cell Li-Ion battery pack engages pack pro-
tection for VBAT less than 5V, this is the lowest voltage
considered for determining the on-time and selecting the
1.5MHz operating frequency.
tON =
5V
1.5MHz • 17V =476ns >tMIN(ON)
Now the switching inductor value is calculated. The induc-
tor value is calculated based on achieving a 30% ripple
current. The ripple current is calculated at the typical input
operating voltage of 17V:
L3 >17V – 8.2V
( )
• 8.2V
1.5MHz • 17V • 30% • 200mA
( )
=48µH
56µH is the next standard inductor value that is greater than
this minimum. This inductor value results in a worst-case
ripple current at the input open-circuit voltage, V
IN(OC)
.
V
IN(OC)
is estimated based on the transmitter design in
Figure4, at the largest coupling coefficient k = 0.37 as:
VIN(OC) = k • n • π • VIN(TX)
VIN(OC) = 0.37 • 3 • 3.14 • 5V = 34.9V
∆IL=34.9V – 8.2V
( )
• 8.2V
1.5MHz • 56µH • 34.9V =75mA
This results in a worst-case peak inductor current of:
IL(PEAK) =ICHG +∆
I
L
2
=237mA
Select an inductor with a saturation current rating greater
than the worst-case peak inductor current of 237mA.
Select a 50V rated capacitor for CIN = 10µF to achieve an
input voltage ripple of 10mV at the typical operating input
voltage of 17V:
∆VIN =
200mA • 8.2V
17V
10µF
=10mV
And select 6V rated capacitors for CINTVCC = 2.2µF,
CBOOST = 22nF, and CBAT = 22µF. Optionally add diode
D6, a 1W, 39V Zener diode if the coupling from trans-
mitter to receiver coils is not well enough controlled to
ensure that VIN remains below 39V when the battery is
fully charged.
LTC4120/LTC4120-4.2
29
Rev. G
For more information www.analog.com
APPLICATIONS INFORMATION
Finally the RUN pin divider is selected to turn on the char-
ger once the input voltage reaches 11.2V. With R3 = 374k
and R4 = 102k the RUN pin reaches 2.4V at VIN = 11.2V.
With this RUN pin divider, the LTC4120 is disabled once
VIN falls below 10.5V.
For this design example, power dissipation during trickle
charge, where the switching charge current is 20mA at
VBAT = 3V and IIN switching = 5mA, is calculated as follows:
PD=20V – 3V
( )
• 10mA +20V • 5mA
+0.3Ω• 0.02A2+0.8Ω•3V
20V • 0.02A2
+0.5Ω• 1– 3V
20V
⎛
⎝
⎜
⎜
⎞
⎠
⎟
⎟• 0.02A2
=
0.27W
This dissipated power results in a junction temperature
rise of:
PD • θJA = 0.27W • 54°C/W = 15°C
During regular charging with VBAT > VTRKL, the power
dissipation reduces to:
PD=20V • 5mA +0.3Ω• 0.2A2
+0.8Ω•8.2V
20V • 0.2A2
+0.5Ω• 1– 8.2V
20V
⎛
⎝
⎜
⎜
⎞
⎠
⎟
⎟• 0.2A2=0.14mW
This dissipated power results in a junction temperature
rise of 6°C over ambient.
Design Example 2: Operation with the LTC4125
The LTC4125 is a 5W AutoResonant wireless power
transmitter that offers several advantages over the simple
transmitter shown in Figure10, including foreign object
detection, external overtemperature detection, automatic
tuning of switching frequency and transmit power. When
operating the LTC4120 receiver with the LTC4125, the
DHC pin serves to enable an external shunt regulator
that optimizes the input supply voltage to the LTC4120
as shown in Figure16. For more information on using the
LTC4125 see the LTC4125 data sheet.
Figure16. LTC4125 Driving a 24μH Transmit Coil at 103kHz, with 1.3A Input Current Threshold, 119kHz Frequency Limit
and 41.5°C Transmit Coil Surface Temperature Limit in a Wireless Power System with LTC4120-4.2 as a 400mA Single
Cell Li-Ion Battery Charger at the Receiver
CTX
100nF
33nF
DTH
FTH
PTHM
IS–
IS+
PTH1
PTH2
EN
NTC
SW1
SW2
FB
LTC4120-4.2
7.87k 59.0k
100k 100k
2.21k
470pF
10nF
10nF
1µF 47µF
x 2
11.3k
20mΩ
4.7nF
0.1µF
CFB1
0.1µF
DC1
DFB
DSTAT
100k
100V
348k
5.23k
24.9k
47µF
LTX
24µH
LRX
47µH
DR2
DR1
VIN
VIN
4.5V
TO
5.5V
10k
10k
+SINGLE
CELL
Li-Ion
BATTERY
PACK
10µF
10nF
2.2µF
DFLZ39
QR1
RNTCRX
RNTCTX
L1
15µH
3.01k
IIN
DC
RC
1k
M1
4120 F16
LTC4125
FAULT
CHRG
BOOST
SW
CHGSNS
BAT
BATSNS
NTC
PROG GND FREQ INTVCC
IMON CTD CTS GND
STATIN IN1 IN2
RUN IN DHC
LTX: 760308100110
CTX: C3216C0G2A104J160AC
CFB1: GRM188R72A104KA35D
DC1: CDBQR70
DSTAT: LTST-C193KGKT-5A
DFB: BAS521-7
RNTCTX: NTHS0603N02N1002J
RED INDICATES HIGH VOLTAGE PARTS
DR1, DR2, DR3: DFLS240L
DC: BZT52C13
M1: Si7308DN
QR1: PMBT3904M
RNTCRX: NTHS0402N02N1002F
LRX: PCB COIL AND FERRITE: B67410-A0223-X195
OR 760308101303
L1: LPS4018-153ML
AIR GAP
3mm
TO
10mm
LTC4120/LTC4120-4.2
30
Rev. G
For more information www.analog.com
PACKAGE DESCRIPTION
3.00 ±0.10
(4 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
1.45 ±0.05
(4 SIDES)
NOTE:
1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
PIN 1
TOP MARK
(NOTE 6)
0.40 ±0.10
BOTTOM VIEW—EXPOSED PAD
1.45 ± 0.10
(4-SIDES)
0.75 ±0.05 R = 0.115
TYP
0.25 ±0.05
1
PIN 1 NOTCH R = 0.20 TYP
OR 0.25 × 45° CHAMFER
15 16
2
0.50 BSC
0.200 REF
2.10 ±0.05
3.50 ±0.05
0.70 ±0.05
0.00 – 0.05
(UD16) QFN 0904
0.25 ±0.05
0.50 BSC
PACKAGE OUTLINE
UD Package
16-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1691 Rev Ø)
LTC4120/LTC4120-4.2
31
Rev. G
For more information www.analog.com
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog
Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications
subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
REVISION HISTORY
REV DATE DESCRIPTION PAGE
A 12/13 Updated Table4 component values and brands. 20
B 03/14 Removed word “battery” from float voltage range bullet.
Modified various specification limits and removed some temp dots.
Modified frequency range, resistor values and Note 3.
Amended IIN curves.
Modified text to reflect typical fOSC values.
Updated text for VPROG servo.
Amended equation for fD.
Modified ICHG equation.
Changed description of End-Of-Charge indication.
Modified typical fOSC values.
Modified Resonant Converter Selection.
Added high voltage pre-regulator schematic.
Added Table4: Recommended Transmitter and High Voltage Pre-Regulator Components.
Added Table5: Recommended Receiver Components.
Added Figure11, PCB Layout of Rx Coil.
Added Figure12, Tx layout: photo of Demo Circuit 1968A.
Added Figure13, Rx layout: photo of Demo Circuit 1967A-B
Modified text of fOSC and fT.
Modified fT equation.
Modified equation for tON, L3, ∆IL, and IL(PEAK) and changed power dissipation calculations.
1
3
4
7
8
9
14
15
16
17
20
20
20
20
20
20
20
23
28
29
C 05/14 Increased minimum VIN to 12.5V
Added fixed 4.2V float version, throughout document, also added electrical parameters for –4.2
Increased IFB specification to TYP 25nA
Reduced min RECHG threshold to –38mV
Modified VPROG servo voltage spec by +3mV and –3mV
Loosened VTRKL threshold voltage spec by –20mV and +10mV
Increased TYP VTRKL hysteresis spec to 50mV
Changed conditions on ISW specification to IN = Open-Circuit from IN = Float
Revised RSNS current limit typical performance characteristics curve
Added typical VFLOAT performance characteristics curve
Corrected error in IIN(SWITCHING) Current curve (x-axis)
Added Block Diagram of –4.2 BATSNS connections
Changed VIN labels to IN in Figure4, 5, and 10
Remove SW inductor selection Tables 6, 7, 8, and 9
Changed location of BAT decoupling cap in Figure15 with reverse blocking diode
Corrected error in L3 equation and substituted correct 56µH inductor
1, 3
1 to 32
3
3
3
4
4
4
5
6
8
11
12, 13, 20
N/A
25
28
D 01/15 Change CBAT from 10µF to 22µF
Add Würth P/N for RX coil
Add INTER-TECH P/N for TX and RX coils
Remove dos on 68µ bias inductor in basic TX schematic for clarity
1, 9, 10, 11, 14, 25,
26, 29 and 32
22
21, 22
12, 20
E 05/15 Clarified Battery Charge Current vs Temperature curve
Clarified End-of-Charge and Battery Recharge sections
Modified Operation without an Input Supply section
Enhanced Reverse Blocking section
Modified INTVCC Supply and Capacitor section
6
16
18
25,26
26
F 02/16 Removed INTVCC spec. Moved Note 4 to UV_INTVCC spec.
Modified INTVCC pin definition.
Included LTC4125 in Applications Information.
Added 4.99k Note.
Added paragraph and Figure16 from LTC4125 data sheet.
Renumbered Figure17. Added to Related Parts Table.
3
9
24
25
29
32
G 11/18 Removed references to PowerByProxi. 12, 27
LTC4120/LTC4120-4.2
32
Rev. G
For more information www.analog.com
ANALOG DEVICES, INC. 2013-2018
11/18
www.analog.com
RELATED PARTS
TYPICAL APPLICATION
PART NUMBER DESCRIPTION COMMENTS
AN138 Wireless Power Users Guide
LTC3335 Nanopower Buck-Boost with
Intergrated Coulomb Counter 680nA Input Quiescent Current (Output in Regulation at No Load) 1.8V to 5.5V Input Operating Range,
Up to 50mA of Output Current, Up to 90% Efficiency
LT3650-8.2/
LT3650-8.4 Monolithic 2A Switch Mode
Non-Synchronous 2-Cell Li-Ion
Battery Charger
Standalone 9V ≤ VIN ≤ 32V (40V Absolute Maximum), 1MHz, 2A Programmable Charge Current, Timer
or C/10 Termination, Small and Few External Components, 3mm × 3mm DFN-12 Package “-8.2” for 2×
4.1V Float Voltage Batteries, “-8.4” for 2× 4.2V Float Voltage Batteries
LT3650-4.1/
LT3650-4.2 Monolithic 2A Switch Mode
Non-Synchronous 1-Cell Li-Ion
Battery Charger
Standalone 4.75V ≤ VIN ≤ 32V (40V Absolute Maximum), 1MHz, 2A Programmable Charge Current,
Timer or C/10 Termination, Small and Few External Components, 3mm × 3mm DFN-12 Package “-4.1”
for 4.1V Float Voltage Batteries, “-4.2” for 4.2V Float Voltage Batteries
LT3652HV Power Tracking 2A Battery
Charger Input Supply Voltage Regulation Loop for Peak Power Tracking in (MPPT) Solar Applications Standalone,
4.95V ≤ VIN ≤ 34V (40V Absolute Maximum), 1MHz, 2A Charge Current, 3.3V ≤ VOUT ≤ 18V. Timer or
C/10 Termination, 3mm × 3mm DFN-12 Package and MSOP-12 Packages
LTC4070 Li-Ion/Polymer Shunt Battery
Charger System Low Operating Current (450nA), 1% Float Voltage Accuracy Over Full Temperature and Shunt Current
Range, 50mA Maximum Internal Shunt Current (500mA with External PFET), Pin Selectable Float
Voltages: 4.0V, 4.1V, 4.2V. Ultralow Power Pulsed NTC Float Conditioning for Li-Ion/Polymer Protection,
8-Lead (2mm × 3mm) DFN and MSOP
LTC4071 Li-Ion/Polymer Shunt Battery
Charger System with Low
Battery Disconnect
Integrated Pack Protection, <10nA Low Battery Disconnect Protects Battery From Over-Discharge. Low
Operating Current (550nA), 1% Float Voltage Accuracy Over Full Temperature and Shunt Current Range,
50mA Maximum Internal Shunt Current, Pin Selectable Float Voltages: 4.0V, 4.1V, 4.2V. Ultralow Power
Pulsed NTC Float Conditioning for Li-Ion/Polymer Protection, 8-Lead (2mm × 3mm) DFN and MSOP
LTC4065/
LTC4065A Standalone Li-Ion Battery
Charger in 2mm × 2mm DFN 4.2V ±0.6% Float Voltage, Up to 750mA Charge Current ; “A” Version Has /ACPR Function. 2mm × 2mm
DFN Package
LTC4123 25mA NiMH Wireless
Charger-Receiver Low Minimum Input Voltage: 2.2V, Temperature Compensated Charge Voltage
LTC4125 5W AutoResonant Wireless
Power Transmitter Monolithic AutoResonant Full Bridge Driver. Transmit Power Automatically Adjusts to Receiver Load,
Foreign Object Detection, Wide Operating Switching Frequency Range: 50kHz to 250kHz, Input Voltage
Range 3V to 5.5V, 20-Lead 4mm × 5mm QFN Package
Figure17. Resonant Coupled Power Transfer Charger Application
INTVCC
IN
RUN
FREQ
CHRG
FAULT
2k BOOST
SW
CHGSNS
DHC
RPROG
6.04k
4120 F17
Li-Ion
T
CBST
22nF
C2S
26.7nF
C2P
6.5nF
LR
47µH
LX
5µH
CIN
10µF
D8 D5 D6
OPT
D9
CINTVCC
2.2µF
CBAT
22µF
VFLOAT
8.2V
LSW
56µH
NTC
PROG
LTC4120
GND
BAT
FB
FBG
RFB1
2.00M
RFB2
825k
10k
+
2k
374k
102k
D5, D8, D9: DFLS240L
D6: MMSZ5259BT1G OR DFLZ39 (OPT)
LSW: SLF6028-470MR59
T: NTHS0402N02N1002F
Tx CIRCUITRY