LTC4002
1
4002f
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
APPLICATIO S
U
FEATURES
TYPICAL APPLICATIO
U
DESCRIPTIO
U
■
Portable Computers
■
Charging Docks
■
Handheld Instruments
■
Wide Input Supply Range:
4.7V to 22V – 4.2 Version
8.9V to 22V – 8.4 Version
■
High Efficiency Current Mode PWM Controller with
500kHz Switching Frequency
■
±1% Charge Voltage Accuracy
■
End-of-Charge Current Detection Output
■
3 Hour Charge Termination Timer
■
Constant Switching Frequency for Minimum Noise
■
±5% Charge Current Accuracy
■
Low 10µA Reverse Battery Drain Current
■
Automatic Battery Recharge
■
Automatic Shutdown When Input Supply is Removed
■
Automatic Trickle Charging of Low Voltage Batteries
■
Battery Temperature Sensing and Charge
Qualification
■
Stable with Ceramic Output Capacitor
■
8-Lead SO and 10-Lead DFN Packages
Standalone Li-Ion
Switch Mode Battery Charger
The LTC
®
4002 is a complete battery charger controller for
one (4.2V) or two (8.4V) cell lithium-ion batteries. With a
500kHz switching frequency, the LTC4002 provides a
small, simple and efficient solution to fast charge Li-Ion
batteries from a wide range of supply voltages. An external
sense resistor sets the charge current with ±5% accuracy.
An internal resistor divider and precision reference set the
final float voltage to 4.2V per cell with ±1% accuracy.
When the input supply is removed, the LTC4002 automati-
cally enters a low current sleep mode, dropping the battery
drain current to 10µA. An internal comparator detects the
near end-of-charge condition while an internal timer sets
the total charge time and terminates the charge cycle. After
the charge cycle ends, if the battery voltage drops below
4.05V per cell, a new charge cycle will automatically begin.
The LTC4002 is available in the 8-lead SO and 10-lead DFN
packages.
6.8µH
22µF
+
4002 TA01
NTC: DALE NTHS-1206N02
10µF
0.1µF
0.47µF
2.2k
68mΩ
Li-Ion
BATTERY
10k
NTC
SENSE
GATE
BAT
CHRG
LTC4002ES8-4.2
VCC
VIN
5V TO 22V
BAT
NTC GND
COMP
2k
CHARGE
STATUS
T
1.5A Single Cell Li-Ion Battery Charger
INPUT VOLTAGE (V)
5
EFFICIENCY (%)
80
V
BAT
= 4V
90
25
4002 TA02
70
60 10 15 20
100
V
BAT
= 3.8V
(CURVES INCLUDE
INPUT DIODE)
Efficiency vs Input Voltage
LTC4002
2
4002f
Supply Voltage (V
CC
) .............................................. 24V
GATE .................................................. (V
CC
–8V) to V
CC
BAT, SENSE .............................................. – 0.3V to 14V
CHRG, NTC ................................................. – 0.3V to 8V
ORDER PART
NUMBER
Consult LTC Marketing for parts specified with wider operating temperature ranges.
LTC4002EDD-4.2
LTC4002EDD-8.4
ABSOLUTE AXI U RATI GS
W
WW
U
PACKAGE/ORDER I FOR ATIO
UUW
(Note 1)
T
JMAX
= 125°C, θ
JA
= 110°C/W
1
2
3
4
8
7
6
5
TOP VIEW
NTC
SENSE
BAT
CHRG
COMP
V
CC
GATE
GND
S8 PACKAGE
8-LEAD PLASTIC SO
DD PART MARKING
LAGG
LBGY
Operating Temperature Range (Note 4) .. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 125°C
Lead Temperature (S8 Package)
(Soldering, 10 sec) ........................................... 300°C
TOP VIEW
11
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
10
9
6
7
8
4
5
3
2
1NC
NTC
SENSE
BAT
CHRG
COMP
V
CC
GATE
PGND
SGND
ORDER PART
NUMBER
LTC4002ES8-4.2
LTC4002ES8-8.4
S8 PART MARKING
400242
400284
ELECTRICAL CHARACTERISTICS
(LTC4002-4.2) The ● denotes the specifications which apply over the full
operating temperature range, otherwise specifications are at TA = 25°C. VCC = 10V unless otherwise noted.
T
JMAX
= 125°C, θ
JA
= 43°C/W
EXPOSED PAD IS GND (PIN 11)
MUST BE SOLDERED TO PCB
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
DC Characteristics
V
CC
V
CC
Supply Voltage ●4.7 22 V
I
CC
V
CC
Supply Current Current Mode 3 5 mA
Shutdown Mode 3 5 mA
Sleep Mode 10 20 µA
V
BAT(FLT)
Battery Regulated Float Voltage 5V ≤ V
CC
≤ 22V (Note 2) 4.168 4.2 4.232 V
●4.158 4.242 V
V
SNS(CHG)
Constant Current Sense Voltage 3V ≤ V
BAT
≤ 4V (Note 3) 0°C ≤ T
A
≤ 85°C●93 100 107 mV
–40°C ≤ T
A
≤ 85°C●90 110 mV
V
SNS(TRKL)
Trickle Current Sense Voltage V
BAT
= 0V (Note 3) 5 10 15 mV
V
TRKL
Trickle Charge Threshold Voltage V
BAT
Rising 2.75 2.9 3.05 V
V
UV
V
CC
Undervoltage Lockout Threshold Voltage V
CC
Rising 3.9 4.2 4.5 V
∆V
UV
V
CC
Undervoltage Lockout Hysteresis Voltage 200 mV
V
MSD
Manual Shutdown Threshold Voltage COMP Pin Falling 200 360 500 mV
V
ASD
Automatic Shutdown Threshold Voltage V
CC
– V
BAT
250 mV
I
COMP
COMP Pin Output Current V
COMP
= 1.2V 100 µA
I
CHRG
CHRG Pin Weak Pull-Down Current V
CHRG
= 1V 15 25 35 µA
V
CHRG
CHRG Pin Output Low Voltage I
CHRG
= 1mA 0.15 0.3 V
R
EOC
End-of-Charge Ratio V
SNS(EOC)
/V
SNS(CHG)
10 25 32 %
t
TIMER
Charge Time Accuracy 10 %
LTC4002
3
4002f
ELECTRICAL CHARACTERISTICS
(LTC4002-4.2) The ● denotes the specifications which apply over the full
operating temperature range, otherwise specifications are at TA = 25°C. VCC = 10V unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
I
NTC
NTC Pin Output Current V
NTC
= 0.85V ●75 85 95 µA
V
NTC-HOT
NTC Pin Threshold Voltage (Hot) V
NTC
Falling ●340 355 370 mV
Hysteresis 25 mV
V
NTC-COLD
NTC Pin Threshold Voltage (Cold) V
NTC
Rising ●2.428 2.465 2.502 V
Hysteresis 170 mV
∆V
RECHRG
Recharge Battery Voltage Offset from Full V
BAT(FULLCHARGED)
– V
RECHRG
, V
BAT
Falling 100 150 200 mV
Charged Battery Voltage
I
LEAK
CHRG Pin Leakage Current V
CHRG
= 8V, Charging Stops 1 µA
Oscillator
f
OSC
Switching Frequency 450 500 550 kHz
DC Maximum Duty Cycle 100 %
Gate Drive
t
r
Rise Time C
GATE
= 2000pF, 10% to 90% 20 ns
t
f
Fall Time C
GATE
= 2000pF, 90% to 10% 50 ns
∆V
GATE
Output Clamp Voltage V
CC
– V
GATE
, V
CC
≥ 9V ●8V
∆V
GATEHI
Output High Voltage ∆V
GATEHI
= V
CC
– V
GATE
, V
CC
≥ 7V ●0.3 V
∆V
GATELO
Output Low Voltage ∆V
GATELO
= V
CC
– V
GATE
, V
CC
≥ 7V ●4.5 V
(LTC4002-8.4) The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at
TA = 25°C. VCC = 12V unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
DC Characteristics
V
CC
V
CC
Supply Voltage ●8.9 22 V
I
CC
V
CC
Supply Current Current Mode 3 5 mA
Shutdown Mode 3 5 mA
Sleep Mode 10 20 µA
V
BAT(FLT)
Battery Regulated Float Voltage 9V ≤ V
CC
≤ 22V (Note 2) 8.336 8.4 8.464 V
●8.316 8.484 V
V
SNS(CHG)
Constant Current Sense Voltage 95 100 105 mV
6V ≤ V
BAT
≤ 8V (Note 3) ●93 100 107 mV
V
SNS(TRKL)
Trickle Current Sense Voltage V
BAT
= 0V (Note 3) 5 10 15 mV
V
TRKL
Trickle Charge Threshold Voltage V
BAT
Rising 4.7 5 5.3 V
V
UV
V
CC
Undervoltage Lockout Threshold Voltage V
CC
Rising 7.5 8.5 V
∆V
UV
V
CC
Undervoltage Lockout Hysteresis Voltage 500 mV
V
MSD
Manual Shutdown Threshold Voltage COMP Pin Falling 200 350 500 mV
V
ASD
Automatic Shutdown Threshold Voltage V
CC
– V
BAT
250 mV
I
COMP
COMP Pin Output Current V
COMP
= 1.2V 100 µA
I
CHRG
CHRG Pin Weak Pull-Down Current V
CHRG
= 1V 15 25 35 µA
V
CHRG
CHRG Pin Output Low Voltage I
CHRG
= 1mA 0.15 0.3 V
R
EOC
End-of-Charge Ratio V
SNS(EOC)
/V
SNS(CHG)
51015 %
t
TIMER
Charge Time Accuracy 10 %
I
NTC
NTC Pin Output Current V
NTC
= 0.85V ●75 85 95 µA
LTC4002
4
4002f
ELECTRICAL CHARACTERISTICS
(LTC4002-8.4) The ● denotes the specifications which apply over the full
operating temperature range, otherwise specifications are at TA = 25°C. VCC = 12V unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
NTC-HOT
NTC Pin Threshold Voltage (Hot) V
NTC
Falling ●340 355 370 mV
Hysteresis 25 mV
V
NTC-COLD
NTC Pin Threshold Voltage (Cold) V
NTC
Rising ●2.428 2.465 2.502 V
Hysteresis 170 mV
∆V
RECHRG
Recharge Battery Voltage Offset from Full V
BAT(FULLCHARGED)
– V
RECHRG
, V
BAT
Falling 200 300 400 mV
Charged Battery Voltage
I
LEAK
CHRG Pin Leakage Current V
CHRG
= 8V, Charging Stops 1 µA
Oscillator
f
OSC
Switching Frequency 450 500 550 kHz
DC Maximum Duty Cycle 100 %
Gate Drive
t
r
Rise Time C
GATE
= 2000pF, 10% to 90% 20 ns
t
f
Fall Time C
GATE
= 2000pF, 90% to 10% 50 ns
∆V
GATE
Output Clamp Voltage V
CC
– V
GATE
●8V
∆V
GATEHI
Output High Voltage ∆V
GATEHI
= V
CC
– V
GATE
●0.3 V
∆V
GATELO
Output Low Voltage ∆V
GATELO
= V
CC
– V
GATE
●4.5 V
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Supply Current vs Temperature Supply Current vs VCC
Oscillator Frequency
vs Temperature
TEMPERATURE (°C)
–50
I
CC
(mA)
3.5
4.0
25 75
4002 G01
3.0
–25 0 50 100 125
2.5
V
CC
(V)
5
I
CC
(mA)
3
25
4002 G02
210 15 20
4CURRENT MODE
TEMPERATURE (°C)
–50
f
OSC
(kHz)
25
4002 G03
500
–25 0 50
450
550
75 100 125
TA = 25°C, VCC = 10V unless otherwise noted.
Note 1: Absolute Maximum Rating are those values beyond which the life
of a device may be impaired.
Note 2: The LTC4002 is tested with Test Circuit 1.
Note 3: The LTC4002 is tested with Test Circuit 2.
Note 4: The LTC4002 is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
LTC4002
5
4002f
TYPICAL PERFOR A CE CHARACTERISTICS
UW
TA = 25°C, VCC = 10V unless otherwise noted.
Oscillator Frequency vs VCC
V
CC
(V)
5
f
OSC
(kHz)
500
25
4002 G04
490 10 15 20
510
CHRG Pin Output Low Voltage
vs VCC
V
CC
(V)
5
V
CHRG
(mV)
140
25
4002 G06
130 10 15 20
150 I
LOAD
= 1mA
Undervoltage Lockout Threshold
vs Temperature
TEMPERATURE (°C)
–50
V
UV
(V)
25
4002 G05
6
–25 0 50
4
8
5
7
75 100 125
V
CC
RISING
LTC4002-8.4
LTC4002-4.2
CHRG Pin Output Low Voltage
vs Temperature
TEMPERATURE (°C)
–50
V
CHG
(mV)
25
4002 G07
140
–25 0 50
100
180
75 100 125
I
LOAD
= 1mA
CHRG Pin Weak Pull-Down
Current vs Temperature
CHRG Output Pin Weak Pull-Down
Current vs VCC
TEMPERATURE (°C)
–50
I
CHRG
(µA)
25
4002 G08
25
–25 0 50
21
29
75 100 125
V
CHRG
= 8V
VCC (V)
5
22
ICHRG (µA)
25
28
10 15 20 25
4002 G09
VCHRG = 8V
Recharge Voltage Offset
Per Cell from Full Charged
Voltage vs Temperature
Recharge Voltage Offset from Full
Charged Voltage vs VCC
TEMPERATURE (°C)
–50
∆V
RECHRG/CELL
(mV)
25
4002 G10
150
–25 0 50
110
190
75 100 125
V
CC
(V)
5
∆V
RECHRG
(mV)
150
25
4002 G11
140 10 15 20
160 LTC4002-4.2
Recharge Voltage Offset from Full
Charged Voltage vs VCC
V
CC
(V)
5
∆V
RECHRG
(mV)
300
25
4002 G12
280 10 15 20
320 LTC4002-8.4
LTC4002
6
4002f
Current Mode Sense Voltage
vs Temperature
TEMPERATURE (°C)
–50
V
SNS
(mV)
25
4002 G13
100
–25 0 50
96
104
75 100 125
Current Mode Sense Voltage
vs VCC
V
CC
(V)
5
V
SNS
(mV)
100
25
4002 G14
98 10 15 20
102 V
BAT
= 4V
LTC4002-4.2
Current Mode Sense Voltage
vs VCC
V
CC
(V)
5
V
SNS
(mV)
100
25
4002 G15
98 10 15 20
102 V
BAT
= 8V
LTC4002-8.4
COMP Pin Output Current
vs VCC
V
CC
(V)
5
I
COMP
(µA)
100
25
4002 G16
98 10 15 20
102 V
COMP
= 0V
COMP Pin Output Current
vs Temperature
TEMPERATURE (°C)
–50
I
COMP
(µA)
25
4002 G17
100
–25 0 50
96
104
75 100 125
V
COMP
= 0V
NTC Pin Output Current
vs VCC
V
CC
(V)
5
I
NTC
(µA)
85
25
4002 G18
84 10 15 20
86 V
NTC
= 0V
TYPICAL PERFOR A CE CHARACTERISTICS
UW
TA = 25°C, VCC = 10V unless otherwise noted.
Trickle Charge Voltage
vs Temperature
Trickle Charge Voltage
vs VCC
TEMPERATURE (°C)
–50
V
TRKL
(V)
25
4002 G19
2.9
–25 0 50
2.8
3.0
75 100 125
LTC4002-4.2
V
CC
(V)
5
V
TRKL
(V)
2.9
25
4002 G20
2.8 10 15 20
3.0 LTC4002-4.2
Trickle Charge Voltage
vs Temperature
TEMPERATURE (°C)
–50
V
TRKL
(V)
25
4002 G21
5.0
–25 0 50
4.8
5.2
75 100 125
LTC4002-8.4
LTC4002
7
4002f
TYPICAL PERFOR A CE CHARACTERISTICS
UW
TA = 25°C, VCC = 10V unless otherwise noted.
Trickle Charge Voltage
vs VCC
V
CC
(V)
5
V
TRKL
(V)
5.0
25
4002 G22
4.8 10 15 20
5.2 V
BAT
= 4V
LTC4002-8.4
Trickle Charge Sense Voltage
vs Temperature Trickle Charge Sense Voltage
vs VCC
TEMPERATURE (°C)
–50
V
SNS
(mV)
25
4002 G23
10.0
–25 0 50
9.6
10.4
75 100 125
V
BAT
= 2.5V
LTC4002-4.2
V
CC
(V)
5
V
SNS
(mV)
10
25
4002 G24
910 15 20
11 V
BAT
= 2.5V
LTC4002-4.2
Trickle Charge Sense Voltage
vs Temperature
Trickle Charge Sense Voltage
vs VCC
TEMPERATURE (°C)
–50
V
SNS
(mV)
25
4002 G25
10.0
–25 0 50
9.6
10.4
75 100 125
V
BAT
= 4V
LTC4002-8.4
V
CC
(V)
5
V
SNS
(mV)
10
25
4002 G26
910 15 20
11 V
BAT
= 4V
LTC4002-8.4
NTC Pin Output Current
vs Temperature
TEMPERATURE (°C)
–50
I
NTC
(µA)
25
4002 G27
85
–25 0 50
81
89
75 100 125
V
NTC
= 0V
End-of-Charge Ratio
vs VCC
VCC (V)
5
22
REOC (%)
25
28
10 15 20 25
4002 G29
LTC4002-4.2
End-of-Charge Ratio
vs Temperature
TEMPERATURE (°C)
–50
R
EOC
(%)
25
4002 G28
25
–25 0 50
21
29
75 100 125
LTC4002-4.2
LTC4002
8
4002f
TYPICAL PERFOR A CE CHARACTERISTICS
UW
TA = 25°C, VCC = 10V unless otherwise noted.
End-of-Charge Ratio
vs Temperature
TEMPERATURE (°C)
–50
R
EOC
(%)
25
4002 G30
10
–25 0 50
6
7
8
9
14
13
12
11
75 100 125
LTC4002-8.4
End-of-Charge Ratio
vs VCC
V
CC
(V)
5
R
EOC
(%)
10 15 20 25
4002 G31
10
6
7
8
9
14
13
12
11
LTC4002-8.4
UU
U
PI FU CTIO S
COMP (Pin 1/Pin 1): Compensation, Soft-Start and Shut-
down Control Pin. The COMP pin is the control signal of the
inner loop of the current mode PWM. Charging begins when
the COMP pin reaches 800mV. The recommended compen-
sation components are a 0.47µF (or larger) capacitor and
a 2.2k series resistor. A 100µA current into the compen-
sation capacitor also sets the soft-start slew rate. Pulling
the COMP pin below 360mV will shut down the charger.
V
CC
(Pin 2/Pin 2): Positive Supply Voltage Input. V
CC
can
range from V
BAT(FLT)
+ 0.5V to 22V. A 0.1µF or higher ca-
pacitor is required at the V
CC
pin with the lead length kept
to a minimum. A 10µF low ESR capacitor is also required
at the source pins of the power P-channel MOSFET.
GATE (Pin 3/Pin 3): Gate Drive Output. Driver Output for
the P-Channel MOSFET. The voltage at this pin is internally
clamped to 8V below V
CC
, allowing a low voltage MOSFET
with gate-to-source breakdown voltage of 8V or less to be
used.
PGND, SGND, Exposed Pad, GND (Pins 4, 5, 11/Pin 4):
IC Ground. The exposed pad (DFN) must be soldered to PCB
ground to provide both electrical contact and optimum
thermal performance.
CHRG (Pin 6/Pin 5): Open-Drain Charge Status Output.
When the battery is being charged, the CHRG pin is pulled
low by an internal N-channel MOSFET. When the charge
current drops below the End-of-Charge threshold for more
than 120µs, the N-channel MOSFET turns off and a 25µA
current source is connected from the CHRG pin to GND.
When the timer runs out or the input supply is removed,
the 25µA current source is turned off and the CHRG pin
becomes high impedance.
BAT (Pin 7/Pin 6): Battery Sense Input. A bypass capaci-
tor of 22µF is required to minimize ripple voltage. An
internal resistor divider, which is disconnected in sleep
mode, sets the final float voltage at this pin. If the battery
connection is opened when charging, an overvoltage
circuit will limit the charger output voltage to 10% above
the programmed float voltage.
When V
BAT
is within 250mV of V
CC
, the LTC4002 is forced
into sleep mode, dropping I
CC
to 10µA.
SENSE (Pin 8/Pin 7): Current Amplifier Sense Input. A sense
resistor, R
SENSE
, must be connected between the SENSE
and BAT pins. The maximum charge current is equal to
100mV/R
SENSE
.
NTC (Pin 9/Pin 8): NTC (Negative Temperature Coefficient)
Thermistor Input. With an external 10kΩ NTC thermistor
to ground, this pin senses the temperature of the battery
pack and stops the charger when the temperature is out of
range. When the voltage at this pin drops below 355mV at
(DFN/SO-8)
LTC4002
9
4002f
UU
U
PI FU CTIO S
(DFN/SO-8)
hot temperature or rises above 2.465V at cold temperature,
charging is suspended and the internal timer stops. The
CHRG pin output is not affected during this hold state. To
disable the temperature qualification function, ground the
NTC pin.
NC (Pin 10/NA): No Connect.
BLOCK DIAGRA
W
–
+
+–
C
EOC
25mV or 10mV
DRIVER
+–
100mV SENSE
–
+
CA
–
+
VA
–
+
C
LB
–
+
C
OV
–
+
C
RQ
–
+
C
COLD
–
+
C
HOT
–
+
GATE
BAT
4.2V/CELL
2.9V OR 5V
4.62V/CELL
4.05V/CELL
2.465V
355mV
50mV
4002 BD
NTC
V
CC
85µA
TEMP
RQ
UV
LOGIC
NTC_DISABLE
EOC
STOP
SD
C/10
UVLO
4.2V
R
R
S
CLK:
Q
–
+
C
PWM
R
SLOP
I
L
I
SLOP
100µA
R
IL
M1
M2
M3
V
CC
COMP
CHRG
GND
–
+
C
SD
360mV
Q4
Q5
25µA
90µA
LTC4002
10
4002f
TEST CIRCUITS
Test Circuit 1 Test Circuit 2
–
+
–
+
100µA
LTC4002
SENSE
BAT
VBAT
4002 TC01
RSENSE
10Ω
CA
COMP
0V
LT1006
15V
1.5V
–
+
–
+
100µA
LTC4002
SENSE
BAT
4.2V
4002 TC02
R
SENSE
10Ω
CA
–
+
VA
COMP
0V
LT1006
15V
1.5V
1mA
OPERATIO
U
The LTC4002 is a constant current, constant voltage
Li-Ion battery charger controller that uses a current mode
PWM step-down (buck) switching architecture. The charge
current is set by an external sense resistor (R
SENSE
)
across the SENSE and BAT pins. The final battery float
voltage is internally set to 4.2V per cell. For batteries like
lithium-ion that require accurate final float voltage, the
internal 2.465V reference, voltage amplifier and the resis-
tor divider provide regulation with ±1% accuracy.
A charge cycle begins when the voltage at the V
CC
pin rises
above the UVLO level and is 250mV or more greater than
the battery voltage. At the beginning of the charge cycle,
if the battery voltage is less than the trickle charge thresh-
old, 2.9V for the 4.2 version and 5V for the 8.4 version, the
charger goes into trickle charge mode. The trickle charge
current is internally set to 10% of the full-scale current. If
the battery voltage stays low for 30 minutes, the battery
is considered faulty and the charge cycle is terminated.
When the battery voltage exceeds the trickle charge thresh-
old, the charger goes into the full-scale constant current
charge mode. In constant current mode, the charge cur-
rent is set by the external sense resistor R
SENSE
and an
internal 100mV reference; I
BAT
= 100mV/R
SENSE
.
When the battery voltage approaches the programmed
float voltage, the charge current will start to decrease.
When the current drops to 25% (4.2 version) or 10% (8.4
version) of the full-scale charge current, an internal com-
parator turns off the internal pull-down N-channel MOSFET
at the CHRG pin, and connects a weak current source to
ground to indicate a near end-of-charge condition.
An internal 3 hour timer determines the total charge time.
After a time out occurs, the charge cycle is terminated
and the CHRG pin is forced high impedance. To restart
the charge cycle, remove and reapply the input voltage or
momentarily shut the charger down. Also, a new charge
cycle will begin if the battery voltage drops below the
recharge threshold voltage of 4.05V per cell.
When the input voltage is present, the charger can be shut
down (I
CC
= 3mA) by pulling the COMP pin low. When the
input voltage is not present, the charger goes into sleep
LTC4002
11
4002f
APPLICATIO S I FOR ATIO
WUUU
Undervoltage Lockout (UVLO)
An undervoltage lockout circuit monitors the input voltage
and keeps the charger off until V
CC
rises above the UVLO
threshold (4.2V for the 4.2 version, 7.5V for the 8.4
version) and at least 250mV above the battery voltage. To
prevent oscillation around the threshold voltage, the UVLO
circuit has 200mV per cell of built-in hysteresis. When
specifying minimum input voltage requirements, the volt-
age drop across the input blocking diode must be added
to the minimum V
CC
supply voltage specification.
Trickle Charge and Defective Battery Detection
At the beginning of a charge cycle, if the battery voltage is
below the trickle charge threshold, the charger goes into
trickle charge mode with the charge current reduced to
10% of the full-scale current. If the low-battery voltage
persists for 30 minutes, the battery is considered defec-
tive, the charge cycle is terminated and the CHRG pin is
forced high impedance.
Shutdown
The LTC4002 can be shut down by pulling the COMP pin
to ground which pulls the GATE pin high turning off the
external P-channel MOSFET. When the COMP pin is re-
leased, the internal timer is reset and a new charge cycle
starts. In shutdown, the output of the CHRG pin is high
impedance and the quiescent current remains at 3mA.
Removing the input power supply will put the charger
into sleep mode. If the voltage at the V
CC
pin drops below
(V
BAT
+ 250mV) or below the UVLO level, the LTC4002
goes into a low current (I
CC
= 10µA) sleep mode, reducing
the battery drain current.
CHRG Status Output Pin
When a charge cycle starts, the CHRG pin is pulled to
ground by an internal N-channel MOSFET which is capable
of driving an LED. When the charge current drops below
the End-of-Charge threshold for more than 120µs, the
N-channel MOSFET turns off and a weak 25µA current
source to ground is connected to the CHRG pin. This weak
25µA pull-down remains until the timer ends the charge
cycle, or the charger is in manual shutdown or sleep mode.
After a time out occurs (charge cycle ends), the pin will
become high impedance. By using two different value re-
sistors, a microprocessor can detect three states from this
pin (charging, end-of-charge and charging stopped) see
Figure 1.
VCC
2k
390k
VDD
OUTCHRG
µPROCESSORLTC4002
IN
4002 F02
Figure 1. Microprocessor Interface
OPERATIO
U
mode, dropping I
CC
to 10µA. This will greatly reduce the
current drain on the battery and increase the standby time.
A 10kΩ NTC (negative temperature coefficient) thermistor
can be connected from the NTC pin to ground for battery
temperature qualification. The charge cycle is suspended
when the temperature is outside of the 0°C to 50°C
window (with DALE NTHS-1206N02).
To detect the charge mode, force the digital output pin,
OUT, high and measure the voltage at the CHRG pin. The
N-channel MOSFET will pull the pin low even with a 2k
pull-up resistor. Once the charge current drops below the
End-of-Charge threshold, the N-channel MOSFET is turned
off and a 25µA current source is connected to the CHRG
pin. The IN pin will then be pulled high by the 2k resistor
connected to OUT. Now force the OUT pin into a high
LTC4002
12
4002f
impedance state, the current source will pull the pin low
through the 390k resistor. When the internal timer has
expired, the CHRG pin changes to a high impedance state
and the 390k resistor will then pull the pin high to indicate
charging has stopped.
Gate Drive
The LTC4002 gate driver can provide high transient cur-
rents to drive the external pass transistor. The rise and fall
times are typically 20ns and 50ns respectively when
driving a 2000pF load, which is typical for a P-channel
MOSFET with R
DS(ON)
in the range of 50mΩ.
A voltage clamp is added to limit the gate drive to 8V below
V
CC
. For example, if V
CC
is 10V then the GATE output will
pull down to 2V max. This allows low voltage P-channel
MOSFETs with superior R
DS(ON)
to be used as the pass
transistor thus increasing efficiency.
Stability
Both the current loop and the voltage loop share a com-
mon, high impedance, compensation node (COMP pin). A
series capacitor and resistor on this pin compensates both
loops. The resistor is included to provide a zero in the loop
response and boost the phase margin.
The compensation capacitor also provides a soft-start
function for the charger. Upon start-up, the COMP pin
voltage will quickly rise to 0.22V, due to the 2.2k series
resistor, then ramp at a rate set by the internal 100µA pull-
up current source and the external capacitor. Battery
charge current starts ramping up when the COMP pin
voltage reaches 0.8V and full current is achieved with the
COMP pin at 1.3V. With a 0.47µF capacitor, time to reach
full charge current is about 2.35ms. Capacitance can be
increased up to 1µF if a longer start-up time is needed.
Automatic Battery Recharge
After the 3 hour charge cycle is completed and both the
battery and the input power supply (wall adapter) are still
connected, a new charge cycle will begin if the battery
voltage drops below 4.05V per cell due to self-discharge
or external loading. This will keep the battery capacity at
more than 80% at all times without manually restarting the
charge cycle.
Battery Temperature Detection
A negative temperature coefficient (NTC) thermistor
located close to the battery pack can be used to monitor
battery temperature and will not allow charging unless the
battery temperature is within an acceptable range.
Connect a 10kΩ thermistor (DALE NTHS-1206N02) from
the NTC pin to ground. If the temperature rises to 50°C, the
resistance of the NTC will be approximately 4.1kΩ. With
the 85µA pull-up current source, the Hot temperature
voltage threshold is 350mV. For Cold temperature, the
voltage threshold is set at 2.465V which is equal to 0°C
(R
NTC
≅ 28.4kΩ) with 85µA of pull-up current. If the
temperature is outside the window, the GATE pin will be
pulled up to V
CC
and the timer frozen while the output
status at the CHRG pin remains the same. The charge cycle
begins or resumes once the temperature is within the
acceptable range. Short the NTC pin to ground to disable
the temperature qualification feature.
APPLICATIO S I FOR ATIO
WUUU
LTC4002
13
4002f
Input and Output Capacitors
Since the input capacitor is assumed to absorb all input
switching ripple current in the converter, it must have an
adequate ripple current rating. Worst-case RMS ripple cur-
rent is approximately one-half of output charge current.
Actual capacitance value is not critical. Solid tantalum
capacitors have a high ripple current rating in a relatively
small surface mount package, but caution must be used
when tantalum capacitors are used for input bypass. High
input surge currents can be created when the adapter is
hot-plugged to the charger and solid tantalum capacitors
have a known failure mechanism when subjected to very
high turn-on surge currents. Selecting the highest pos-
sible voltage rating on the capacitor will minimize prob-
lems. Consult with the manufacturer before use.
The selection of output capacitor C
OUT
is primarily deter-
mined by the ESR required to minimize ripple voltage and
load step transients. The output ripple ∆V
OUT
is approxi-
mately bounded by:
∆≤∆ +
⎛
⎝
⎜⎞
⎠
⎟
V I ESR fC
OUT L OSC OUT
1
8
Since ∆I
L
increases with input voltage, the output ripple is
highest at maximum input voltage. Typically, once the ESR
requirement is satisfied, the capacitance is adequate for
filtering and has the necessary RMS current rating.
APPLICATIO S I FOR ATIO
WUUU
Switching ripple current splits between the battery and the
output capacitor depending on the ESR of the output ca-
pacitor and the battery impedance. EMI considerations
usually make it desirable to minimize ripple current in the
battery leads. Ferrite beads or an inductor may be added
to increase battery impedance at the 500kHz switching
frequency. If the ESR of the output capacitor is 0.2Ω and
the battery impedance is raised to 4Ω with a bead or induc-
tor, only 5% of the current ripple will flow in the battery.
Design Example
As a design example, take a charger with the following
specifications: V
IN
= 5V to 22V, V
BAT
= 4V nominal, I
BAT
=
1.5A, f
OSC
= 500kHz, see Figure 2.
First, calculate the SENSE resistor :
R
SENSE
= 100mV/1.5A = 68mΩ
Choose the inductor for about 65% ripple current at the
maximum V
IN
:
LV
kHz A
V
VH=
()()()
⎛
⎝
⎜⎞
⎠
⎟=µ
4
500 0 65 1 5 14
22 6 713
.. –.
Selecting a standard value of 6.8µH results in a maximum
ripple current of :
∆=
()
µ
()
⎛
⎝
⎜⎞
⎠
⎟=IV
kHz H
V
VmA
L4
500 6 8 14
22 962 6
.–.
LTC4002
14
4002f
APPLICATIO S I FOR ATIO
WUUU
Next, choose the P-channel MOSFET. The Si6435ADQ in
a TSSOP-8 package with R
DS(ON)
= 42mΩ (nom), 55mΩ
(max) offers a small solution. The maximum power dissi-
pation with V
IN
= 5V and V
BAT
= 4V at 50°C ambient
temperature is:
PAmV
VW
D
=
()
Ω
()()
=
1 5 55 4
50 099
2
..
T
J
= 50°C + (0.099W)(65°C/W) = 56.5°C
C
IN
is chosen for an RMS current rating of about 0.8A at
85°C. The output capacitor is chosen for an ESR similar to
the battery impedance of about 100mΩ. The ripple voltage
on the BAT pin is:
VI ESR
AmV
OUT RIPPLE LMAX
()()
..
=∆
()
=
()
Ω
()
=
2
096 01
248
C1: Taiyo Yuden TMK325BJ106MM
C2: Taiyo Yuden JMK325BJ226MM
L1: TOKO B952AS-6R8N
The Schottky diode D2 shown in Figure 2 conducts current
when the pass transistor is off. In a low duty cycle case, the
current rating should be the same or higher than the
charge current. Also it should withstand reverse voltage as
high as V
IN
.
Board Layout Suggestions
When laying out the printed circuit board, the following
considerations should be taken to ensure proper opera-
tion of the LTC4002.
GATE pin rise and fall times are 20ns and 50ns respectively
(with C
GATE
= 2000pF). To minimize radiation, the catch
diode, pass transistor and the input bypass capacitor
traces should be kept as short as possible. The positive
side of the input capacitor should be close to the source of
the P-channel MOSFET; it provides the AC current to the
pass transistor. The connection between the catch diode
and the pass transistor should also be kept as short as
possible. The SENSE and BAT pins should be connected
directly to the sense resistor (Kelvin sensing) for best
charge current accuracy. Avoid routing the NTC PC board
trace near the MOSFET switch to minimize coupling switch-
ing noise into the NTC pin.
The compensation capacitor connected at the COMP pin
should return to the ground pin of the IC or as close to it
as possible. This will prevent ground noise from disrupt-
ing the loop stability. The ground pin also works as a heat
sink, therefore use a generous amount of copper around
the ground pin. This is especially important for high V
CC
and/or high gate capacitance applications.
L1
6.8µH
+
4002 F02
NTC: DALE NTHS-1206N02
CC
0.47µF
RC
2.2k
4.2V
Li-Ion
BATTERY
10k
NTC
SENSE
GATE
BAT
CHRG
LTC4002ES8-4.2
VCC
VIN
5V TO 22V
BAT
NTC GND
COMP
R1
2k
CHARGE
STATUS
T
M1
Si6435ADQ
2
3
7
61
5
48
D1
B330
D2
B330
C2
22µF
CER
C1
10µF
CER
C3
0.1µF
CER
RSENSE
68mΩ
Figure 2. 1.5A Single Cell Li-Ion Battery Charger
LTC4002
15
4002f
U
PACKAGE DESCRIPTIO
3.00 ±0.10
(4 SIDES)
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
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
0.38 ± 0.10
BOTTOM VIEW—EXPOSED PAD
1.65 ± 0.10
(2 SIDES)
0.75 ±0.05
R = 0.115
TYP
2.38 ±0.10
(2 SIDES)
15
106
PIN 1
TOP MARK
(SEE NOTE 6)
0.200 REF
0.00 – 0.05
(DD10) DFN 1103
0.25 ± 0.05
2.38 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
1.65 ±0.05
(2 SIDES)2.15 ±0.05
0.50
BSC
0.675 ±0.05
3.50 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.016 – .050
(0.406 – 1.270)
.010 – .020
(0.254 – 0.508)× 45°
0°– 8° TYP
.008 – .010
(0.203 – 0.254)
SO8 0303
.053 – .069
(1.346 – 1.752)
.014 – .019
(0.355 – 0.483)
TYP
.004 – .010
(0.101 – 0.254)
.050
(1.270)
BSC
1234
.150 – .157
(3.810 – 3.988)
NOTE 3
8765
.189 – .197
(4.801 – 5.004)
NOTE 3
.228 – .244
(5.791 – 6.197)
.245
MIN .160 ±.005
RECOMMENDED SOLDER PAD LAYOUT
.045 ±.005
.050 BSC
.030 ±.005
TYP
INCHES
(MILLIMETERS)
NOTE:
1. DIMENSIONS IN
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
LTC4002
16
4002f
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2003
LT/TP 1104 1K PRINTED IN USA
TYPICAL APPLICATIO
U
2-Cell 8.4V, 2A Li-Ion Battery Charger
L1
6.8µH
D2
B330
M1
1/2 Si9933ADY
M2
1/2 Si9933ADY
C2
22µF
CER
4002 TA03
NTC: DALE NTHS-1206N02
C1
10µF
CER
C3
0.1µF
CER
C
C
0.47µF
R
C
2.2k
R
SENSE
50mΩ
8.4V
Li-Ion
BATTERY
10k
NTC
SENSE
GATE 3
2
7
61
5
84
BAT
CHRG
LTC4002ES8-8.4
V
CC
V
IN
9V TO 12V
NTC GND
COMP
R1
100k
T
+
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