LTC4040
1
4040fb
For more information www.linear.com/LTC4040
Typical applicaTion
FeaTures DescripTion
2.5A Battery Backup
Power Manager
The LT C
®
4040 is a complete 3.5V to 5.5V supply rail bat-
tery backup system. It contains a high current step-up
DC/DC regulator to back up the supply from a single-cell
Li-Ion or LiFePO4 battery. When external power is avail-
able, the step-up regulator operates in reverse as a step-
down battery charger
.
The LTC4040’s adjustable input current limit function
reduces charge current to protect the main supply from
overload while an external disconnect switch isolates the
external supply during backup. When the input supply
drops below the adjustable PFI threshold, the 2.5A boost
regulator delivers power from the battery to the system
output.
An optional input overvoltage protection (OVP) circuit
protects the LTC4040 from high voltage damage at the
VIN pin. One logic input selects either the Li-Ion or the
LiFePO4 battery option, and two other logic inputs pro-
gram the battery charge voltage to one of four levels suit-
able for backup applications. The LTC4040 is available in a
low profile (0.75mm) 24-Lead 4mm × 5mm QFN package.
4.5V Backup Application with 4.22V PFI Threshold
(Charge Current Setting: 1A, Input Current Limit Setting: 2A)
Normal to Backup Mode Transition Waveform
applicaTions
n Step-Up Backup Supply and Step-Down Battery
Charger
n 6.5A Switches for 2.5A Backup from 3.2V Battery
n Input Current Limit Prioritizes Load Over Charge
Current
n Input Disconnect Switch Isolates Input During Backup
n Automatic Seamless Switch-Over to Backup Mode
n Input Power Loss Indicator
n System Power Loss Indicator
n Pin Selectable Battery: Li-Ion (3.95V/4.0V/4.05V/4.1V)
or LiFePO4 (3.45V/3.5V/3.55V/3.6V)
n Optional OVP Circuitry Protects Device to >60V
n Constant Frequency Operation
n Low Profile (0.75mm) 24-Lead 4mm × 5mm QFN Package
n Fleet and Asset Tracking
n Automotive GPS Data Loggers
n Automotive Telematics Systems
n Toll Collection Systems
n Security Systems
n USB Powered Devices
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
and PowerPath is a trademark of Analog Devices, Inc. All other trademarks are the property
of their respective owners. Protected by U.S. Patents, including 6522118, 6570372, 6700364,
8139329.
+
324k
2.2µH
VSYS
PROGBSTOFFCHGOFF F2F1F0
IGATE
LTC4040
VIN CLN
1500k
4.5V
12mΩ
10µF
100µF
2.2µF
SYSTEM
LOAD
BSTFB
RSTFB
4.5V INPUT
SUPPLY
SW
BAT
NTC
NTC
VSYS
2k
LiFePO4
3.6V
4040 TA01a
VIN
OVSNS
PFI
FAULT
PFO
RST
CHRG
CLPROG
154k
60.4k
1A
V
SYS
V
IN
I
BAT
V
BAT
= 3.3V
R
= 2k
I
SYS
= 1A
C
SYS
= 100µF
TIME (ms)
–0.4
0
0.4
0.8
1.2
–1
0
1
2
3
4
5
–2
0
2
4
6
8
10
VOLTAGE (V)
CURRENT (A)
Waveform (LiFePO
4
App.)
Normal to Backup Mode Transition
4040 TA01b
LTC4040
2
4040fb
For more information www.linear.com/LTC4040
pin conFiguraTionabsoluTe MaxiMuM raTings
VIN (Transient) t < 1ms, Duty Cycle < 1% .... –0.3V to 7V
VIN (Steady State), BAT, CLN, VSYS,
BSTFB, NTC, OVSNS,
CHRG, PFO, RST, FA U LT ............................... –0.3V to 6V
F0, F1, F2, BSTOFF, RSTFB,
PFI, CHGOFF ......–0.3V to Max (VIN, VBAT, VSYS) + 0.3V
IOVSNS .................................................................. ±10mA
ICHRG, IPFO, IRST, IFAU LT .......................................... 10mA
IPROG, ICLPROG....................................................... 1.1mA
Operating Junction Temperature Range
(Note 3) ...................................................... –40 to 125°C
Storage Temperature Range ...................... –65 to 125°C
(Notes 1, 2)
8 9
TOP VIEW
25
GND
UFD PACKAGE
24-LEAD (4mm × 5mm) PLASTIC QFN
10 11 12
24 23 22 21 20
6
5
4
3
2
1
VSYS
PROG
CLPROG
CHGOFF
BSTOFF
VIN
CLN
PFI
BSTFB
NTC
OVSNS
IGATE
F0
F1
VSYS
BAT
SW
SW
PF0
CHRG
FAULT
RSTFB
RST
F2
7
14
15
16
17
18
19
13
TJMAX = 125°C, θJA = 43°C/W
EXPOSED PAD (PIN 25) IS GND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC4040EUFD#PBF LTC4040EUFD#TRPBF 4040 24-Lead (4mm × 5mm × 0.75mm) Plastic QFN –40°C to 125°C
LTC4040IUFD#PBF LTC4040IUFD#TRPBF 4040 24-Lead (4mm × 5mm × 0.75mm) Plastic QFN –40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on nonstandard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
http://www.linear.com/product/LTC4040#orderinfo
LTC4040
3
4040fb
For more information www.linear.com/LTC4040
elecTrical characTerisTics
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. (Note 3) VIN = 5V, VBAT = 3.6V, RPROG = 2k, unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Input Voltage Range l3.5 5.5 V
VBAT Battery Voltage Range (Backup Boost Input) 2.7 5 V
IINQ VIN Quiescent Current Normal Mode (VPFI = 2V), Battery Charger Timed Out
Shutdown (BSTOFF = CHGOFF=1)
570
3.5
7
µA
µA
IBATQ BAT Quiescent Current Normal Mode (VPFI = 2V), Battery Charger Timed Out
Backup Mode (VIN = VPFI = 0V), No System Load
Shutdown (BSTOFF = CHGOFF = 1)
l
45
40
1.5
70
3
µA
µA
µA
Battery Charger
VCHG
BAT Regulated Output Voltage for LiFePO4
Option (F2 = 0)
F2 = 0, F1 = 0, F0 = 0
F2 = 0, F1 = 0, F0 = 1
F2 = 0, F1 = 1, F0 = 0
F2 = 0, F1 = 1, F0 = 1
l
l
l
l
3.42
3.47
3.52
3.57
3.45
3.50
3.55
3.60
3.48
3.53
3.58
3.63
V
V
V
V
BAT Regulated Output Voltage for Li-Ion
Option (F2 = 1)
F2 = 1, F1 = 0, F0 = 0
F2 = 1, F1 = 0, F0 = 1
F2 = 1, F1 = 1, F0 = 0
F2 = 1, F1 = 1, F0 = 1
l
l
l
l
3.92
3.97
4.02
4.07
3.95
4.00
4.05
4.10
3.98
4.03
4.08
4.13
V
V
V
V
ICHG Regulated Battery Charge Current RPROG = 2k 950 1000 1050 mA
VSYS-to-VBAT Differential Undervoltage
Lockout Threshold (Falling)
40 50 60 mV
VSYS-to-BAT Differential Undervoltage
Lockout Threshold (Rising)
125 145 165 mV
VPROG PROG Pin Servo Voltage 800 mV
hPROG Ratio of Battery Current to PROG Pin Current 2500 mA/
mA
ITRKL Trickle Charge Current VBAT = 2.5V, RPROG = 2k 125 mA
PROG Pin Servo Voltage at Trickle Charge VBAT = 2.5V, RPROG = 2k 100 mV
Input Current Limit Threshold Voltage VIN – VCLN l23.5 25 26.5 mV
ACLPROG Input Current Limit Amplifier Gain Ratio of CLPROG Voltage to (VIN – VCLN) 32 V/V
CLN Input Bias Current VCLN = VIN 300 nA
VRECHG Recharge Battery Threshold Voltage Threshold Voltage Relative to VCHG if F2 = 0 and F1 = 1
Threshold Voltage Relative to VCHG All Other Cases
94.2
96.7
95
97.5
95.8
98.3
%
%
tTERMINATE Safety Timer Termination Period Timer Starts When VBAT = VCHG
F2 = 1 (Li-Ion)
F2 = 0 (LiFePO4)
3.7
1.85
4.25
2.13
5
2.5
Hours
Hours
VLOWBAT Low Battery Threshold Voltage for Trickle Charge VBAT Rising 2.75 2.85 2.95 V
�VLOWBAT Low Battery Hysteresis 150 mV
tBADBAT Bad-Battery Termination Time VBAT < (VLOWBAT − ΔVLOWBAT) 0.47 0.54 0.64 Hours
VC/8 End-of-Charge Indication PROG Pin Average Voltage 90 100 110 mV
fOSC(BUCK) Step-Down (Buck) Converter Switching
Frequency
Normal Mode (VPFI > 1.21V) 1.96 2.25 2.65 MHz
RP(BUCK) High Side Switch On-Resistance Normal Mode (VPFI > 1.21V) 130 mΩ
RN(BUCK) Low Side Switch On-Resistance Normal Mode (VPFI > 1.21V) 120 mΩ
ILIM(BUCK) PMOS Switch Current Limit 3 4.3 A
LTC4040
4
4040fb
For more information www.linear.com/LTC4040
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. (Note 3) VIN = 5V, VBAT = 3.6V, RPROG = 2k, unless otherwise noted.
elecTrical characTerisTics
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
NTC
VCOLD Cold Temperature Fault Threshold Voltage Rising Voltage Threshold
Hysteresis
75.0 76.5
1.5
78 %VIN
%VIN
VHOT Hot Temperature Fault Threshold Voltage Falling Voltage Threshold
Hysteresis
33.4 34.9
1.73
36.4 %VIN
%VIN
VDIS NTC Disable Threshold Voltage Falling Threshold
Hysteresis
0.7 1.7
50
2.7 %VIN
mV
INTC NTC Leakage Current –20 20 nA
Backup Mode Boost Switching Regulator
VBSTFB BSTFB Reference Voltage l0.78 0.8 0.82 V
IBSTFB BSTFB Input Bias Current –20 20 nA
VSYS Step-up (Boost) Converter Output Voltage
Range
3.5 5 V
fOSCBST Step-Up Converter Switching Frequency Backup Mode (VPFI < 1.17V) 0.98 1.125 1.33 MHz
ILIMBST NMOS Switch Current Limit 5.5 6.5 7.5 A
RPBST Boost High Side Switch On-Resistance 75 mΩ
RNBST Boost Low Side Switch On-Resistance 70 mΩ
VOVSD VSYS Overvoltage Shutdown Threshold VSYS Rising 5.3 5.5 5.7 V
Overvoltage Shutdown Hysteresis 100 mV
VUVLO BAT Pin Undervoltage Lockout VBAT Falling 2.45 2.6 V
BAT Pin Undervoltage Lockout Hysteresis 150 mV
DMAX Maximum Boost Duty Cycle 88 93 %
NMOS Switch Leakage BSTOFF = 1, CHGOFF = 1 1 µA
PMOS Switch Leakage BSTOFF = 1, CHGOFF = 1 1 µA
Reset Comparator
RSTFB Threshold (Falling) l0.72 0.74 0.76 V
RSTFB Hysteresis 20 mV
RSTFB Pin Leakage Current VRSTFB = 0.9V –50 50 nA
RST Delay (RSTFB Rising) 232 ms
Power-Fail Comparator
PFI Input Threshold (Falling Edge) Initiates Backup Mode l1.17 1.19 1.21 V
PFI Input Hysteresis 30 mV
PFI Pin Leakage Current VPFI = 1.3V –100 100 nA
PFI Delay to PFO PFI Falling 0.5 µs
PFO Pin Leakage Current VPFO = 5V 10 µA
PFO Pin Output Low Voltage IPFO = 5mA 65 mV
Logic Input (CHGOFF, BSTOFF, F0, F1, F2)
VIL Logic Low Input Voltage l0.4 V
VIH Logic High Input Voltage l1.2 V
IIL Logic Low Input Leakage –1 1 µA
IIH Logic High Input Leakage –1 1 µA
LTC4040
5
4040fb
For more information www.linear.com/LTC4040
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. (Note 3) VIN = 5V, VBAT = 3.6V, RPROG = 2k, unless otherwise noted.
elecTrical characTerisTics
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Open-Drain Output (CHRG, RST, FAULT)
Pin Leakage Current V = 5V 1 µA
Pin Output Low Voltage I = 5mA 65 mV
Overvoltage Protection
VOV(CUTOFF) Overvoltage Protection Threshold Rising Threshold, ROVSNS = 6.2k 6.1 6.4 6.7 V
VOVGT IGATE Output Voltage Active Input Voltage < VOV(CUTOFF) 1.88 •
VOVSNS
12 V
VOVGT(LOAD)
IGATE Voltage Under Load 5V Through 6.2k Into OVSNS, IIGATE = 1µA 8 8.6 V
IOVSNSQ OVSNS Quiescent Current VOVSNS = 5V 40 µA
OVSNS Quiescent Current at Shutdown BSTOFF = H, CHGOFF = H 25 µA
IGATE Time to Reach Regulation CIGATE = 2.2nF 3.5 ms
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: This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
Note 3: The LTC4040E is tested under pulsed load conditions such that
TJ ≈ TA. The LTC4040E is guaranteed to meet performance specifications
from 0°C to 85°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process control. The
LTC4040I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The junction temperature (TJ in °C) is calculated from
the ambient temperature (TA, in °C) and power dissipation (PD, in watts)
according to the formula:
TJ = TA + (PD • θJA)
where the package thermal impedance θJA = 43°C/ W.
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 resistance and
other environmental factors.
LTC4040
6
4040fb
For more information www.linear.com/LTC4040
Typical perForMance characTerisTics
TA = 25°C, unless otherwise noted.
R
= 2k
V
SYS
= 5V
F2 = 1, F1 = 0, F0 = 0
F2 = 1, F1 = 0, F0 = 1
F2 = 1, F1 = 1, F0 = 0
F2 = 1, F1 = 1, F0 = 1
V
BAT
(V)
2.7
3
3.3
3.6
3.9
4.2
0
200
400
600
800
1000
I
BAT
(mA)
Different Charge Voltage Settings
I
BAT
vs V
BAT
(Li–Ion) with
4040 G01
R
= 2k
V
SYS
= 5V
F2 = 0, F1 = 0, F0 = 0
F2 = 0, F1 = 0, F0 = 1
F2 = 0, F1 = 1, F0 = 0
F2 = 0, F1 = 1, F0 = 1
V
BAT
(V)
2.7
2.9
3.1
3.3
3.5
3.7
0
200
400
600
800
1000
I
BAT
(mA)
Different Charge Voltage Settings
I
BAT
vs V
BAT
(LiFePO
4
) with
4040 G02
VBAT (V)
2.8
3.0
3.2
3.4
3.6
3.8
4.0
60
65
70
75
80
85
90
95
100
EFFICIENCY (%)
vs VBAT
Step–Down Charger Efficiency
4040 G03
RPROG = 4k
RPROG = 2k
RPROG = 1.33k
RPROG = 1k
RPROG = 0.8k
V
SYS
= 5V
F2 = F1 = F0 = 1
R
= 0.8k
R
= 1k
R
= 1.33k
R
= 2k
R
= 4K
V
SYS
= 5V
F2, F1, F0 = 1
V
BAT
(V)
2.7
3.0
3.3
3.6
3.9
4.2
0
500
1000
1500
2000
2500
3000
I
BAT
(mA)
Different PROG Resistor Values
I
BAT
vs V
BAT
(Li–Ion) with
4040 G04
V
SYS
= 5V
F2 = 0, F1 = F0 = 0
R
= 0.8k
R
= 1k
R
= 1.33k
R
= 2k
R
= 4k
V
BAT
(V)
2.7
2.9
3.1
3.3
3.5
3.7
0
500
1000
1500
2000
2500
3000
I
BAT
(mA)
Different PROG Resistor Values
I
BAT
vs V
BAT
(LiFePO
4
) with
4040 G05
VSYS = 5V
F2 = F1 = F0 = 1
TEMPERATURE (°C)
–50
–30
–10
10
30
50
70
90
110
130
3.70
3.75
3.80
3.85
3.90
3.95
4.00
4.05
4.10
4.15
4.20
VBAT (V)
vs Temperature
Battery Charge Voltage (Li-Ion)
4040 G06
V
BAT
= 3.2V
V
IN
= 5.5V
V
IN
= 5.0V
V
IN
= 3.6V
TEMPERATURE (°C)
–45
–10
25
60
95
130
1.80
1.90
2.00
2.10
2.20
2.30
FREQUENCY (MHz)
Frequency vs Temperature
Step–Down Charger Oscillator
4040 G07
130°C
90°C
60°C
25°C
–10°C
–45°C
V
SYS
(V)
3.6
3.8
4
4.2
4.4
4.6
4.8
5.0
80
100
120
140
160
180
200
RESISTANCE (mΩ)
vs V
SYS
over Temperature
Step–Down Charger PMOS R
ds(ON)
4040 G08
130°C
90°C
60°C
25°C
–10°C
–45°C
V
SYS
(V)
3.6
3.8
4
4.2
4.4
4.6
4.8
5.0
80
100
120
140
160
180
200
RESISTANCE (mΩ)
vs V
SYS
over Temperature
Step–Down Charger NMOS R
DS(ON)
4040 G09
Step-Down Charger Efficiency
vs VBAT
IBAT vs VB AT (Li-Ion) with Different
PROG Resistor Values
IBAT vs VB AT (LiFePO4) with
Different PROG Resistor Values
Battery Charge Voltage (Li-Ion)
vs Temperature
Step-Down Charger Oscillator
Frequency vs Temperature
Step-Down Charger PMOS
On-Resistance vs VSYS over
Temperature
Step-Down Charger NMOS
On-Resistance vs VSYS over
Temperature
IBAT vs VB AT (Li-Ion) with Different
Charge Voltage Settings
IBAT vs VB AT (LiFePO4) with
Different Charge Voltage Settings
LTC4040
7
4040fb
For more information www.linear.com/LTC4040
Typical perForMance characTerisTics
TA = 25°C, unless otherwise noted.
TIME (h)
0
1
2
3
4
5
6
3.00
3.20
3.40
3.60
3.80
4.00
4.20
0
200
400
600
800
1000
1200
BATTERY VOLTAGE (V)
CHARGE CURRENT (mA)
Li–Ion Battery Charging Profile
4040 G10
V
SYS
= 5V
R
= 2k
F2 = F1 = F0 = 1
VBAT
IBAT
V
SYS
= 5V
R
= 2k
F2 = 0, F1 = F0 = 1
TIME (h)
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
3.1
3.2
3.3
3.4
3.5
3.6
3.7
0
200
400
600
800
1000
1200
BATTERY VOLTAGE (V)
CHARGE CURRENT (mA)
LiFePO
4
Battery Charging Profile
4040 G11
SYSTEM LOAD CURRENT (mA)
0
500
1000
1500
2000
2500
0
500
1000
1500
2000
2500
CURRENT (mA)
Input Current Limit Set by R
S
Charge Current Reduction Due to
4040 G12
TOTAL INPUT CURRENT
V
SYS
= 5V
R
= 2k
R
S
= 12 mΩ
I
BAT
V
IN
V
SYS
I
BAT
V
BAT
= 3.6V
I
SYS
= 1A
R
= 2k
C
SYS
= 100µF
TIME (µs)
–500
–250
0
250
500
750
1000
–1
0
1
2
3
4
5
6
–2
0
2
4
6
8
10
12
VOLTAGE (V)
CURRENT (A)
Transition Waveform (Li–Ion)
Normal to Backup Mode
4040 G13
TIME (ms)
–200
–100
0
100
200
300
400
500
600
700
–1
0
1
2
3
4
5
6
–1
0
1
2
3
4
5
6
VOLTAGE (V)
CURRENT (A)
Transition Waveform
Backup to Normal Mode
4040 G14
VSYS
VIN
IBAT
ZERO
VBAT = 3.7V
RPROG = 2k
ISYS = 1A
TIME (µs)
0
200
400
600
800
1000
1200
–2.0
–1.5
–1.0
–0.5
0.0
0.5
1.0
1.5
–1
0
1
2
3
4
5
6
PROG VOLTAGE (V)
CURRENT (A)
to System Step Load
PROG Voltage Transient Response
4040 G15
V
I
SYS
V
BAT
= 3.7V
R
= 2k
R
S
= 12mΩ
I
BAT
Li-Ion Battery Charging Profile LiFePO4 Battery Charging Profile
Charge Current Reduction Due to
Input Current Limit Set by RS
Normal to Backup Mode
Transition Waveform (Li-Ion)
Backup to Normal Mode
Transition Waveform
PROG Voltage Transient Response
by System Step Load
LTC4040
8
4040fb
For more information www.linear.com/LTC4040
VBAT = 3.2V
VBAT = 3.7V
VBAT = 4.1V
LOAD CURRENT (mA)
1
10
100
1k
3k
0
10
20
30
40
50
60
70
80
90
100
EFFICIENCY (%)
vs Load Current
Backup Boost Efficiency
4040 G19
V
SYS
SET TO 5V
130°C
90°C
25°C
–10°C
60°C
–45°C
V
SYS
(V)
3.5
3.8
4.1
4.4
4.7
5.0
50
60
70
80
90
100
110
RESISTANCE (mΩ)
vs V
SYS
over Temperature
Backup Boost NMOS R
DS(ON)
4040 G20
130°C
90°C
60°C
25°C
–10°C
–45°C
V
SYS
(V)
3.5
3.8
4.1
4.4
4.7
5.0
50
60
70
80
90
100
110
RESISTANCE (mΩ)
vs V
SYS
over Temperature
Backup Boost PMOS R
DS(ON)
4040 G21
V
BAT
= 4.1V
V
BAT
= 3.6V
V
BAT
= 2.7V
TEMPERATURE (°C)
–45
–10
25
60
95
130
25
30
35
40
45
CURRENT (µA)
I
BATQ
vs Temperature
SLEEP Mode (Backup)
4040 G22
Typical perForMance characTerisTics
TA = 25°C, unless otherwise noted.
V
SYS
= Set to 5V
V
BAT
= 3.6V
I
SYS
= 1mA
TEMPERATURE (°C)
–45
–10
25
60
95
130
4.50
4.60
4.70
4.80
4.90
5.00
5.10
V
SYS
(V)
(V
SYS
) vs Temperature
Back–Up Boost Output Voltage
4040 G16
V
SYS
= 5V
V
BAT
= 4.1V
V
BAT
= 3.6V
V
BAT
= 2.7V
TEMPERATURE (°C)
–45
–10
25
60
95
130
0.90
0.95
1.00
1.05
1.10
1.15
FREQUENCY (MHz)
Frequency vs Temperature
Backup Boost Oscillator
4040 G17
V
BAT
= 3.6V
TEMPERATURE (°C)
–45
–10
25
60
95
130
80
82
84
86
88
90
MAX DUTY CYCLE (%)
Duty Cycle vs Temperature
Backup Boost Maximum
4040 G18
Back-Up Boost Output Voltage
(VSYS) vs Temperature
Backup Boost Oscillator
Frequency vs Temperature
Backup Boost Maximum
Duty Cycle vs Temperature
Backup Boost Efficiency
vs Load Current
Backup Boost NMOS On-Resistance
vs VSYS over Temperature
Backup Boost PMOS On-Resistance
vs VSYS over Temperature
SLEEP Mode (Backup)
IBATQ vs Temperature
LTC4040
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Typical perForMance characTerisTics
TA = 25°C, unless otherwise noted.
V
BAT
= 3.6V
C
SYS
= 100µF
L = 2.2µH
V
SYS
I
SYS
TIME (ms)
–0.4
0.0
0.4
0.8
1.2
1.6
4.6
4.7
4.8
4.9
5.0
5.1
5.2
5.3
0
1
2
3
4
5
6
7
VOLTAGE (V)
LOAD CURRENT (A)
Response to Load Step
Backup Boost Transient
4040 G23
V
BAT
= 3.6V
C
SYS
= 100µF
L = 2.2µH
I
SYS
V
SYS
TIME (ms)
–0.4
0.0
0.4
0.8
1.2
1.6
4.6
4.7
4.8
4.9
5.0
5.1
5.2
5.3
0
1
2
3
4
5
6
7
VOLTAGE (V)
LOAD CURRENT (A)
Mode Transition Waveform
Burst Mode to Constant Frequency
4040 G24
TEMPERATURE (°C)
–45
–10
25
60
95
130
6.20
6.25
6.30
6.35
6.40
6.45
6.50
VOLTAGE (V)
(Through 6.2k) vs Temperature
OVP Module Shutdown Voltage
4040 G25
TEMPERATURE (°C)
–45
–10
25
60
95
130
30
35
40
45
50
CURRENT (µA)
vs Temperature
OVSNS Pin Quiescent Current
4040 G26
INPUT = 5V
Backup Boost Transient
Response to Load Step
Burst Mode to Constant Frequency
Mode Transition Waveform
OVP Module Shutdown Voltage
(Through 6.2k) vs Temperature
OVSNS Pin Quiescent Current
vs Temperature
LTC4040
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For more information www.linear.com/LTC4040
pin FuncTions
VSYS (Pins 1, 24): System Voltage Output Pin. This pin
is used to provide power to an external load from either
the primary input supply or the backup battery if the pri-
mary input supply is not available. In addition to supplying
power to the load, this pin provides power to charge the
battery when input power is available. VSYS should be
bypassed with a low ESR ceramic capacitor of at least
100µF to GND.
PROG (Pin 2): Charge Current Program Pin. An external
resistor from the PROG pin to ground programs the full-
scale charge current. At full scale, the PROG pin servos
to 0.8V. The ratio of BAT pin current to PROG pin current
is internally set to 2500.
CLPROG (Pin 3): VSYS Current Monitoring Pin. The ratio
between the CLPROG pin voltage and the differential volt-
age between VIN and CLN is internally set to 32. Charge
current is reduced when the CLPROG pin voltage reaches
0.8V.
CHGOFF (Pin 4): Disable Pin for the Battery Charger. Tie
this pin to GND to enable the charger or to a voltage above
1.2V to disable it. Do not leave this pin unconnected.
BSTOFF (Pin 5): Disable Pin for the Backup Boost
Converter. Tie this pin to GND to enable the boost backup
or to a voltage above 1.2V to disable backup. Do not leave
this pin unconnected.
VIN (Pin 6): Input Pin. Power can be applied directly to
this pin if the optional overvoltage protection (OVP) fea-
ture is not used. For applications where the OVP feature
is required, connect an external N-channel FET between
the power supply output VPWR and this pin.
CLN (Pin 7): Negative terminal pin for an external cur-
rent limit sense resistor connected between VIN and this
pin. This resistor is used to monitor the current from
VIN to VSYS. The LT4040 reduces charge current in order
to maintain 25mV across this sense resistor. However,
it does not limit the system current if the drop exceeds
25mV.
CHRG (Pin 8): Open-Drain Charge Status Output; typi-
cally pulled up through a resistor to a reference voltage.
During a battery charging cycle, CHRG is pulled low until
the charge current drops below C/8 when the CHRG pin
becomes high impedance.
FAULT (Pin 9): Open-Drain Fault Status Output; typically
pulled up through a resistor to a reference voltage. This
pin indicates charge cycle fault conditions during a bat-
tery charging cycle. A temperature fault or a bad-battery
fault causes this pin to be pulled low. If no fault conditions
exist, the FAULT pin remains high impedance.
RSTFB (Pin 10): Reset Comparator Input. High Impedance
input to an accurate comparator with a 0.74V falling
threshold and 20mV hysteresis. This pin controls the state
of the RST output pin. An external resistor divider is used
between VSYS, RSTFB and GND. It can be the same resis-
tor divider as the BSTFB divider to monitor the system
output voltage VSYS. See the Applications Information
section.
RST (Pin 11): Open-Drain Status Output of the Reset
Comparator. This pin is pulled to ground by an internal
N-channel MOSFET whenever the RSTFB pin falls below
0.74V. Once the RSTFB pin voltage recovers, the pin
becomes high impedance after a 232ms delay.
F2 (Pin 12): Logic Input to Select Battery Chemistry. A
logic high on this pin selects Li-Ion and a logic low selects
LiFePO4. Do not leave this pin unconnected.
F1, F0 (Pins 13, 14): Logic inputs to select one of the four
possible charge voltage settings for each battery chemis-
try. Do not leave these pins unconnected.
F0 F1 F2 = 1: Li-Ion (V) F2 = 0: LiFePO4 (V)
0 0 3.95 3.45
1 0 4.00 3.50
0 1 4.05 3.55
1 1 4.10 3.60
LTC4040
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For more information www.linear.com/LTC4040
pin FuncTions
IGATE (Pin 15): Gate Pin for the External N-Channel FETs.
This pin is driven by an internal charge pump to develop
sufficient overdrive to fully enhance the pass transistors.
The first pass transistor is connected between the supply
output VPWR and VIN and is part of the optional overvolt-
age protection module. The second pass transistor, con-
nected between VIN and VSYS, is mandatory and is used
to disconnect the system from the input supply during
backup mode.
OVSNS (Pin 16): Overvoltage Protection Sense Input. If
the overvoltage feature is used, the OVSNS pin should be
connected through a 6.2k resistor to an input power con-
nector and the drain of an N-channel MOS pass transistor.
If not, this pin should be shorted to VIN. When voltage is
detected on OVSNS, it draws a small amount of current to
power a charge pump which then provides gate drive to
IGATE to energize the external transistor. When the voltage
on this pin exceeds typically 6V, IGATE is pulled to GND
to disable the pass transistor and protect the LTC4040
from high voltage.
NTC (Pin 17): Input to the Thermistor Monitoring Circuits.
The NTC pin connects to a battery’s thermistor to deter-
mine if the battery is too hot or too cold to charge. If the
battery’s temperature is out of range, charging is paused
until it re-enters the valid range. A low drift bias resistor
is required from VIN to NTC and a thermistor is required
from NTC to ground. If the NTC function is not desired,
the NTC pin should be grounded.
BSTFB (Pin 18): Feedback Input for the Backup Boost
Regulator. During steady-state backup operation, voltage
on this pin servos to 0.8V.
PFI (Pin 19): Power-Fail Input. High impedance input to
an accurate comparator (power-fail) with a 1.19V falling
threshold and 30mV hysteresis. PFI controls the state of
the PFO output pin and sets the input voltage threshold
below which the boost backup is initiated. This threshold
voltage also represents the minimum voltage above which
the step-down battery charger is enabled and the part
allows power to flow from the input to the output through
the external pass transistors.
PFO (Pin 20): Open-Drain Power-Fail Status Output. This
pin is pulled to ground by an internal N-channel MOSFET
when the PFI input is below the falling threshold of the
power-fail comparator. Once the PFI input rises above the
rising threshold, this pin becomes high impedance.
SW (Pins 21, 22): Power Transmission Pin for the Buck
Switching Charger and the Boost Switching Backup
Converter. A 1µH to 2.2µH inductor should be connected
from SW to BAT.
BAT (Pin 23): Single Cell Li-Ion or LiFePO4 Battery Pin.
Depending on the availability of input power, the battery
will either deliver power to VSYS via the boost converter
or be charged from V
SYS
via the buck charger. BAT should
be bypassed with a low ESR ceramic capacitor of at least
10µF to GND.
GND (Exposed Pad Pin 25): The exposed pad must
be soldered to the PCB to provide a low electrical and
thermal impedance connection to the printed circuit
board’s ground. A continuous ground plane on the sec-
ond layer of a multilayer printed circuit board is strongly
recommended.
LTC4040
12
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For more information www.linear.com/LTC4040
block DiagraM
14
13
+
–
+
–
+
–
+
–
CHARGE
VOLTAGE
SELECTOR
F0
23
BAT
2
PROG
CHGOFF
RPROG
RFB2
CBAT
RFB1
F1
12
325
17
F2
4040 F01
8
R1
0.8V
BAD-BATTERY
DETECTOR
6.4k
R5
NTC
FAULT
R4
RBIAS
VIN
RNTC
R3
VIN
PFI
CLPROG
GND
R2
+
–
A4
0.8V
0.8V
BUCK/BOOST
CHARGER
CTRL
BOOST
CTRL
BUCK CHARGER
BOOST BACKUP
+
–
A3
0.8V
+
–
A2
PWM
4
BSTFB 18
RSTFB
VSYS
1, 24
SYSTEM
10
RST
11
7
BSTOFF
5
SW L1
21, 22
0.74V
MN2
MN1
CLN
15
IGATE
RS
6V
VIN
232ms
DELAY
+
–
+–
+
+
–
2.85V
BAT
+
–
C/8 DETECTOR
PROG
0.1V
1.19V
+
–
6
A1
AV = 32
CHARGER
LOGIC
NTC ENABLE
OVERTEMP
UNDERTEMP
0.1V
9
CHRG
8
19
OVSNS
6.2k
INPUT
16
PFO
20
RPF1
RPF2
+
–
+–
CP1
OVERVOLTAGE PROTECTION
A6
Li-Ion/
LiFePO4
BATTERY
VPWR
POWER-FAIL
COMPARATOR
LTC4040
13
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For more information www.linear.com/LTC4040
operaTion
The LTC4040 is a complete battery backup system manager
for a 3.5V to 5.5V supply rail. The system has three princi-
pal circuit components: a full-featured step-down (buck)
battery charger, a step-up (boost) backup converter with
automatic burst feature to deliver power to the system load
when external input power is lost and a power-fail com-
parator to decide which one to activate. The LTC4040 has
several other auxiliary components: an input current limit
(CLPROG) amplifier, an optional input overvoltage protec-
tion (OVP) circuit and a reset comparator.
The LTC4040 has three modes of operation: normal,
backup and shutdown. If the input supply is above an
externally programmable PFI threshold voltage, the part
is considered to be in normal mode in which power flows
from input to output (VSYS) while the step-down switch-
ing regulator charges the battery to one of eight charge
voltage settings programmed by the F0, F1, and F2 digi-
tal inputs. Please refer to the Block Diagram. The total
system load is monitored by the CLPROG amplifier via
an external series resistor, RS, connected between the
VIN and CLN pins. This amplifier can reduce the charge
current from its programmed value (set by the PROG
pin external resistor RPROG) if the external load demand
increases beyond a programmable level set by RS. When
the input supply falls below the PFI threshold, backup
mode disconnects the switches (MN1 and MN2) to iso-
late the system (VSYS) from the input while the boost
converter powers the system load from the battery using
the same external inductor, L1.
THE BATTERY CHARGER
The LTC4040 includes a full-featured constant-current
(CC)/constant-voltage (CV) battery charger with auto-
matic recharge, automatic termination by safety timer,
low voltage trickle charging, bad-battery detection and
thermistor sensor input for out-of-temperature charge
pausing. The battery charger is a high efficiency buck
switching converter used to transfer charge from V
SYS
to BAT via the SW pin. The charger can be disabled by
pulling the CHGOFF pin above 1.2V.
Buck Switching Charger
The LTC4040 battery charger is a constant frequency
(2.25MHz) synchronous buck converter capable of
directly charging the battery to its charge voltage with an
externally programmable charge current up to 2.5A from
an input supply as high as 5.5V. A zero current com-
parator monitors the inductor current and shuts off the
NMOS synchronous rectifier once the current reduces to
approximately 250mA. This prevents the inductor current
from reversing and improves efficiency for low charging
current.
Battery Preconditioning (Trickle Charge)
and Bad-Battery Fault
When a battery charge cycle begins, the battery char-
ger first determines if the battery is deeply discharged. If
the battery voltage is below VLOWBAT, typically 2.85V, an
automatic trickle charge feature sets the charge current
to 1/8th or 12.5% of the programmed value. To improve
charge current accuracy at this low level, the buck switch-
ing charger is turned off and a secondary linear charger
is used to deliver charge to the battery. If the low voltage
persists for more than half an hour, the battery charger
automatically terminates and indicates, via the CHRG and
FAULT pins, that the battery is in bad-battery fault.
Constant-Current Mode Charging
Once the battery voltage is above VLOWBAT, the charger
begins charging in full power constant-current mode. The
current delivered to the battery will try to reach 2000V/
R
PROG
. Depending on the external load condition, the bat-
tery charger may or may not be able to charge at the full
programmed rate. The external load will always be priori-
tized over the battery charge current. The battery charger
will charge at the full programmed rate only if the sum of
the external load and the charger input current is less than
or equal to the input current limit set by RS.
LTC4040
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For more information www.linear.com/LTC4040
operaTion
Charge Termination
The battery charger has a built-in safety timer. Once the
voltage on the battery reaches the charge voltage set by
the F0, F1 and F2 pins, the charger will regulate the battery
voltage there and the charge current will decrease natu-
rally. The safety timer (approximately 4-hour for Li-Ion
and approximately 2-hour for LiFePO
4
batteries) starts
once the charger detects that the battery has reached the
charge voltage. After the safety timer expires, charging
of the battery will discontinue and no more current will
be delivered unless the battery voltage falls below the
automatic recharge threshold.
Automatic Recharge
Once the battery charger terminates, it will remain off
drawing only microamperes of current from the battery. If
the product remains in this state long enough, the battery
will eventually self-discharge. To ensure that the battery is
always topped off, a charge cycle will automatically begin
when the battery voltage falls below VRECHRG. In the event
that the safety timer is running when the battery voltage
falls below VRECHRG, it will reset back to zero. To prevent
brief excursions below VRECHRG from resetting the safety
timer, the battery voltage must be below VRECHG for more
than 2.4ms.
Charge Status Indication via the CHRG and FAULT Pins
The status of the battery charger is indicated via the CHRG
and FAULT pins according to the fallowing table:
Table 1. Charge Status Indication
CHRG FAULT STATUS
0 0 NTC Fault and C/8 Not Reached
0 1 Charging (No Fault)
1 0 Bad Battery Fault
1 1 Charging Nearly Complete – C/8 Reached
When charging begins, CHRG is pulled low and remains
low for the duration of a normal charging cycle. When
charge current drops to 1/8th the value programmed by
RPROG, the CHRG pin is released (Hi-Z). The CHRG pin
does not respond to the C/8 threshold if the LTC4040 is
in input current limit. This prevents false end-of-charge
indications due to insufficient power available to the bat-
tery charger.
If a battery is found to be unresponsive to charging (i.e.,
its voltage remains below 2.85V for more than 1/2 hour),
the CHRG pin will be released and the FAULT pin will be
pulled low, indicating that the charging has been termi-
nated. However, if there is a fault due to NTC, only the
FAULT pin is pulled low while the CHRG pin remains low,
indicating a pause in charging.
Battery Thermal Protection with NTC Thermistor
The LTC4040 monitors the battery temperature during the
charging cycle by using a negative temperature coefficient
(NTC) thermistor, placed close to the battery pack. If the
battery temperature moves outside a safe charging range,
the IC suspends charging and signals a fault condition
until the temperature returns to the safe charging range.
The safe charging range is determined by two compara-
tors that monitor the voltage at the NTC pin as shown
in the Block Diagram. To use this feature, connect the
thermistor, RNTC, between the NTC pin and ground and a
bias resistor, RBIAS, from VIN to NTC. RBIAS should be a
1% resistor with a value equal to the value of the chosen
thermistor at 25°C (R25).
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 ß25/85.
The LTC4040 will pause charging when the resistance of
the thermistor increases to 325% of the RBIAS resistor as
the temperature drops. For a Vishay Curve 2 thermistor
with ß25/85 = 3490K and 25°C resistance of 10k, this cor-
responds to a temperature of about 0°C. The LTC4040 also
pauses charging if the thermistor resistance decreases to
53.6% of the RBIAS resistor. For the same Vishay Curve2
thermistor, this corresponds to approximately 40°C. If the
battery charger is in constant-voltage mode, the safety
timer also pauses until the thermistor indicates a return
to a valid temperature. The hot and cold comparators each
have approximately 2°C of hysteresis to prevent oscilla-
tion about the trip point. Grounding the NTC pin disables
all NTC functionality.
LTC4040
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operaTion
Differential Undervoltage Lockout
An undervoltage lockout circuit monitors the differential
voltage between VSYS and BAT and shuts off the charger if
the BAT voltage reaches within 50mV of the VSYS voltage.
Charging does not resume until this difference increases to
145mV.
BACKUP BOOST CONVERTER
To supply the system load from the battery in backup
mode, the LTC4040 contains a 1.125MHz constant-fre-
quency current-mode synchronous boost switching regu-
lator with output disconnect and automatic Burst Mode
features. The regulator can provide a maximum load of
2.5A from a battery as low as 3.2V and the system output
voltage (VSYS) can be programmed up to a maximum of 5V
via the BSTFB pin. See the Applications Information section
for details. The converter can be disabled by pulling the
BSTOFF pin high. The boost regulator includes safety fea
-
tures like short-circuit current protection, input undervolt-
age lockout, and output overvoltage protection.
Zero Current Comparator
The LTC4040 boost converter includes a zero current
comparator which monitors the inductor current and
shuts off the PMOS synchronous rectifier once the current
drops to approximately 250mA. This prevents the induc-
tor current from reversing in polarity thereby improving
efficiency at light loads.
PMOS Synchronous Rectifier
To prevent the inductor current from running away,
the PMOS synchronous rectifier is only enabled when
VSYS > (VBAT – 200mV). Additionally, if the current through
the synchronous FET (PMOS) ever exceeds 8A, the con-
verter skips the next two clock cycles so that the inductor
current has a chance to discharge safely below this level.
Short-Circuit Protection
The output disconnect feature enables the LTC4040 boost
converter to survive a short circuit at its output. It incor-
porates internal features such as current limit foldback
and thermal shutdown for protection from excessive
power dissipation during short circuit.
VBAT Undervoltage Lockout
To prevent the battery from discharging too deeply, the
LTC4040 incorporates an undervoltage lockout circuit
which shuts down the boost regulator when VBAT drops
below 2.45V.
Boost Overvoltage Protection
If the BSTFB node were inadvertently shorted to ground,
then the boost converter output would increase indefi-
nitely with the maximum current that could be sourced
from BAT. The LTC4040 protects against this by shutting
off both switches if the output voltage exceeds 5.5V.
Burst Mode Operation
To improve battery life during backup, the LTC4040 boost
converter provides automatic Burst Mode operation which
increases the efficiency of power conversion at very light
loads. Burst Mode operation is initiated if the output load
current falls below an internally set threshold. Once Burst
Mode operation is initiated, only the circuitry required
to monitor the output is kept alive. This is referred to
as the sleep state in which the backup boost consumes
only 40µA from the battery. When the VSYS pin voltage
drops by about 1% from its nominal value, the part wakes
up and commences normal PWM operation. The output
capacitor recharges and causes the part to re-enter the
sleep state if the output load remains less than the Burst
Mode threshold. The frequency of this intermittent PWM
or Burst Mode operation depends on the load current;
that is, as the load current drops further below the burst
threshold, the boost converter turns on less frequently.
When the load current increases above the burst thresh-
old, the converter seamlessly resumes continuous PWM
operation. Thus, Burst Mode operation maximizes the
efficiency at very light loads by minimizing switching
and quiescent losses. However, the output ripple typi-
cally increases to about 2% peak-to-peak. Burst Mode
ripple can be reduced, in some circumstances, by plac-
ing a small phase-lead capacitor (CPL) between the VSYS
and BSTFB pins. However, this may adversely affect the
efficiency and the quiescent current at light loads. Typical
values of CPL range from 15pF to 100pF.
LTC4040
16
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For more information www.linear.com/LTC4040
operaTion
VBAT > VSYS Operation
The LTC4040 boost converter will maintain voltage regu-
lation even if its input voltage is above the output voltage.
This is achieved by terminating the switching of the syn-
chronous PMOS and applying VBAT voltage statically on
its gate. This ensures that the slope of the inductor current
will reverse during the time current is flowing to the out-
put. Since the PMOS no longer acts as a low impedance
switch in this mode, there will be more power dissipation
within the IC. This will cause a sharp drop in the efficiency.
The maximum output current should be limited in order
to maintain an acceptable junction temperature.
INPUT CURRENT LIMIT AND CLPROG MONITOR
The LTC4040 contains an input current limit circuit which
monitors the total system current (the external load plus
the charger input current) via an external series resistor,
RS, connected between the pins VIN and CLN. The part
does not actually limit the external load but as the exter-
nal load demand increases, it reduces charge current, if
necessary, in an attempt to maintain a maximum of 25mV
across the V
IN
and CLN pins. Please refer to Programming
the Input Current Limit and CLPROG Monitor section in
Applications Information. However, if the external load
demand exceeds the limit set by R
S
, the part does not
reduce the load current but the charge current will drop
to zero. In all scenarios, the voltage on the CLPROG pin
will correctly represent the total system current. 800mV
on the CLPROG pin represents the full-scale current set
by the external series resistor, RS.
POWER-FAIL COMPARATOR AND MODE SWITCHING
The LTC4040 contains a fast power-fail comparator which
switches the part from normal to backup mode in the
event the input supply voltage falls below an externally
programmed threshold voltage. This threshold voltage
is programmed by an external resistor divider via the PFI
pin. See the Applications Information section for details of
how to choose values for the resistor divider. The output
of the power-fail comparator also directly drives the gate
of an open-drain NMOS to report the status of the avail-
ability of input power via the PFO pin. If input power is
available, the PFO pin is high impedance; otherwise, the
pin is pulled down to ground.
At the onset of backup mode, the battery charger shuts
off, the external NMOS pass transistors (MN1 and MN2
in Block Diagram) are quickly turned off by discharg-
ing IGATE to ground thereby disconnecting the system
output VSYS from the input and the backup boost con-
verter activates promptly to deliver load from the battery.
Although the power-fail comparator has a hysteresis of
approximately 30mV, it may not be able to overcome the
input voltage spike resulting from the sudden collapse of
the forward current from the input to V
SYS
. To prevent
repeated unwanted mode switching, once activated, the
backup boost stays on for at least half a second. During
this time, the power-fail comparator output is ignored and
an internal switch of approximately 270Ω pulls down the
OVSNS pin to help discharge the input. After the half-
second timer expires, if the power-fail comparator output
indicates that power is still not available, the backup boost
continues to deliver the load but the pull-down on the
OVSNS pin is released. When the power-fail compara-
tor detects that input power is available, the OVP charge
pump starts to charge up the IGATE pin but the backup
boost converter continues to deliver system load until
IGATE is approximately 8V. This ensures that the forward
conduction path through the external NFET pass transis-
tors has been established. At this point, the backup boost
gets deactivated and the charger turns back on to charge
the battery while the system load gets delivered directly
from the input to VSYS through the pass transistors.
RESET COMPARATOR
The LTC4040 contains a reset comparator which moni-
tors VSYS under all operating modes via the RSTFB pin
and reports the status via an open-drain NMOS transistor
on the RST pin. At any time, if VSYS falls 7.5% from its
programmed value, the RST pin pulls low almost instan-
taneously. However, the comparator waits approximately
232ms after VSYS rises above the threshold before making
the RST pin high impedance. Please refer to Programming
the Reset Comparator Threshold section in Applications
Information.
LTC4040
17
4040fb
For more information www.linear.com/LTC4040
OPTIONAL INPUT OVERVOLTAGE PROTECTION (OVP)
The LTC4040 can protect itself from the inadvertent
application of excessive voltage with just two external
components: an N-channel FET (MN1) and a 6.2k resis-
tor as shown in the Block Diagram. The maximum safe
overvoltage magnitude will be determined by the choice
of external NMOS and its associated drain breakdown
voltage.
The optional overvoltage protection (OVP) module con-
sists of two pins. The first, OVSNS, is used to measure the
applied voltage through an external resistor. The second,
IGATE, is an output used to drive the gate pins of two exter-
nal N-channel FETs, MN1 and MN2 (Block Diagram). The
voltage at the OVSNS pin will be lower than the OVP input
voltage by about 250mV due to the OVP circuit’s quiescent
current flowing through the OVSNS resistor. When OVSNS
is below 6V, an internal charge pump will drive IGATE
to approximately 1.88 • VOVSNS. This will enhance the
N-channel FETs and provide a low impedance connection
operaTion
to VSYS and power the chip. If OVSNS should rise above
6V due to a fault, IGATE will be pulled down to ground, dis-
abling the external FETs to protect downstream circuitry.
At the same time, the backup boost converter will be acti-
vated to supply the system load from the battery. When
the voltage drops below 6V again, the external FETs will be
re-enabled. If the OVP feature is not desired, remove MN1,
short OVSNS to VIN and apply external power directly to
VIN.
SHUTDOWN MODE OPERATION
The LTC4040 can be shutdown almost entirely by pulling
both CHGOFF and BSTOFF pin above 1.2V. In this mode,
the internal charge pump is shutdown and IGATE is pulled
to ground disconnecting the forward path from input to
output via the external FETs. Only the internal OVP shunt
regulator remains active to monitor the input supply for
any possible overvoltage condition and consumes about
25µA via the OVSNS pin. Total current draw from the BAT
pin drops to below 3µA during shutdown.
LTC4040
18
4040fb
For more information www.linear.com/LTC4040
applicaTions inForMaTion
NUMBER OF CYCLES
CAPACITY
CHARGE VOLTAGE (V)
4
4.1
4.2
4.3
4.4
4.5
0
250
500
750
1000
1250
1500
1750
2000
50
60
70
80
90
100
110
120
130
CHARGE/ DISCHARGE CYCLES
BATTERY CAPACITY (%)
4040 F01
Figure1. Battery Cycle Life and Capacity
as a Function of Charge Voltage
charge voltage to maximize battery lifetime since battery
capacity degrades even faster when batteries remain fully
charged. Because of the different Li-Ion battery chemis-
tries and other conditions that can affect battery lifetime,
the curves shown here are only estimates of the number
of charge cycles and battery-capacity levels.
PROGRAMMING THE INPUT VOLTAGE THRESHOLD
FOR THE POWER-FAIL COMPARATOR
The input voltage threshold below which the power-fail
status pin PFO indicates a power-fail condition and the
LTC4040 activates the backup boost operation can be
programmed by using a resistor divider from the supply
to GND via the PFI pin such that:
VSUPP(PFO) =VPFI •1+RPF1
RPF2
⎛
⎝
⎜⎞
⎠
⎟=1.19V •1+RPF1
RPF2
⎛
⎝
⎜⎞
⎠
⎟
VPFI is approximately 1.19V. See Block Diagram. The PFI
threshold voltage should be set to a level between 200mV
to 300mV below the nominal input supply voltage so that
the supply transients do not trip the comparator. On the
other hand, it should be set high enough so that the VSYS
voltage does not drop too much to trip the reset compara-
tor during the transition to backup mode.
PROGRAMMING THE BATTERY CHARGE CURRENT
Battery charge current is programmed using a single
resistor from the PROG pin to ground. To set a charge
current of ICHG, the PROG pin resistor value can be deter-
mined using the following equation:
RPROG =2500 •
0.8V
I
CHG
=
2000V
I
CHG
For example, to set the charge current to 1A, the value
of the PROG pin resistor should be 2k. The minimum
recommended charge current is 500mA, below which the
accuracy of the charge current suffers. This corresponds
to a maximum RPROG resistor of 4k.
CHOOSING A CHARGE VOLTAGE FOR THE BATTERY:
The LTC4040 offers 4 different charge voltage options for
each of the two battery chemistries (Li-Ion and LiFePO4)
and these levels are selected by the digital inputs F0, F1
and F2. Choosing a higher charge voltage increases the
battery capacity to provide a longer product run-time but
reduces the battery lifetime, usually measured by the
number of charge/ discharge cycles. Battery manufactur-
ers usually consider the end of life for a battery to be when
the battery capacity drops to 80% of the rated capacity.
The curves in Figure1 show the relationship between
cell capacity and cycle life for a typical Li-Ion battery cell.
Using 4.2V as the charge voltage, a typical Li-Ion battery
is considered at 100% initial capacity but delivers about
500 charge/ discharge cycles before the capacity drops
to 80%. However, if the same battery uses 4.1V as the
charge voltage, it is at 85% initial capacity but the number
of charge/discharge cycles can be almost doubled to 1000
before the capacity drops to 80%. Lowering the charge
voltage even further to 4.0V can increase the battery life-
time more than three times to 1800 charge/ discharge
cycles. Since LTC4040 is a backup product, the battery
is likely to spend the majority of its lifetime fully charged.
This makes it even more critical to charge at a lower
LTC4040
19
4040fb
For more information www.linear.com/LTC4040
PROGRAMMING THE INPUT CURRENT LIMIT
AND CLPROG MONITOR
The input current limit is programmed by connecting a
series resistor between the VIN and CLN pins. To limit the
total system current to ISYSLIM, the value of the required
resistor can be calculated using the following equation:
RS=
25mV
ISYSLIM
For example, to set the current limit to 2A, the series
resistor should be 12.5mΩ. As discussed in the
Operations section, the part does not limit the system
current but reduces the charge current to zero in case the
system load exceeds this limit.
The voltage on the CLPROG pin always represents the
total system current ISYS through the external series resis-
tance, RS. 800mV on CLPROG represents the full-scale
current set by RS. The system current can be calculated
from the CLPROG pin voltage by using the following
equation:
ISYS =
V
CLPROG
32•RS
For example, if the CLPROG pin voltage is 600mV and
RS is 12.5mΩ, then the total system current is 1.5A. As
shown in the block diagram, the CLPROG pin is not buff-
ered internally. So it is important to isolate this pin before
connecting to an ADC or any other monitoring device.
Failure to do so would degrade the accuracy of this circuit.
PROGRAMMING THE BOOST OUTPUT VOLTAGE
The boost converter output voltage in backup mode can
be programmed for any voltage from 3.5V to 5V by using
a resistor divider from the VSYS pin to GND via the BSTFB
pin such that:
VSYS =VBSTFB •1+RFB1
R
FB2
⎛
⎝
⎜
⎞
⎠
⎟=0.8V •1+RFB1
R
FB2
⎛
⎝
⎜
⎞
⎠
⎟
VBSTFB is 0.8V. See the Block Diagram. Typical values for
RFB1 and RFB2 are in the range of 40k to 2M. Too small a
resistor will result in a large quiescent current whereas
too large a resistor coupled with any parasitic BSTFB pin
capacitance will create an additional pole and may cause
loop instability.
PROGRAMMING THE RESET COMPARATOR
THRESHOLD
The threshold for the reset comparator can be pro-
grammed by using a resistor divider from the VSYS pin
to GND via the RSTFB pin such that:
VSYS(RST) =VRSTFB •1+RFB1
RFB2
⎛
⎝
⎜
⎞
⎠
⎟=0.74V •1+RFB1
RFB2
⎛
⎝
⎜
⎞
⎠
⎟
VRSTFB is 0.74V. See the Block Diagram. Typical values
for RFB1 and RFB2 are in the range of 40k to 2M. In most
applications, the BSTFB and RSTFB pins can be shorted
together and only one resistor divider between VSYS and
GND is needed to set the VSYS voltage during backup
mode and the reset threshold 7.5% below the VSYS pro-
grammed voltage.
CHOOSING THE EXTERNAL RESISTOR FOR THE
OVERVOLTAGE PROTECTION (OVP) MODULE
In an overvoltage condition, the OVSNS pin will be clamped
at 6V. The external 6.2k resistor must be sized appropri-
ately to dissipate the resultant power. For example, a 1/8W
6.2k resistor can have at most
P
MAX •6.2kΩ = 28V
applied across its terminals. With the 6V at OVSNS, the
maximum overvoltage magnitude that this resistor can
withstand is 34V. A 1/4W 6.2k resistor raises the value to
45V. The OVSNS pin’s absolute maximum current rating
of 10mA imposes an upper limit of 68V protection.
applicaTions inForMaTion
LTC4040
20
4040fb
For more information www.linear.com/LTC4040
CHOOSING THE EXTERNAL TRANSISTORS
(MN1ANDMN2) FOR THE OVP MODULE AND THE
INPUT-TO-OUTPUT DISCONNECT SWITCH
The LTC4040 uses a weak internal charge pump to pump
IGATE above the input voltage so that N-channel exter-
nal FETs can be used as pass transistors. However, these
transistors should be carefully chosen so that they are
fully enhanced with a VGS of 3V. Since one of these pass
transistors is the OVP FET, its breakdown voltage (BVDSS)
determines the maximum voltage the LTC4040 can with-
stand at its input. Also, care must be taken to avoid any
leakage on the IGATE pin, as it may adversely affect the
FET operation. See Table 2 for a list of recommended
transistors.
Table 2. Recommended NMOS FETs for Overvoltage Protection
and Disconnect Switch
NMOS FET BVDSS RON
SIR424DP (Vishay) 20V 7.4mΩ
SiS488DN (Vishay) 40V 7.5mΩ
SiS424DN (Vishay) 20V 8.9mΩ
CHOOSING THE INDUCTOR FOR THE SWITCHING
REGULATORS
Since the same inductor is used to charge the battery in
normal mode and to deliver the system load in backup
mode, its inductance should be low enough so that the
inductor current can reverse quickly as soon as the
backup mode is initiated. On the other hand, the induc-
tance should not be so low that the inductor current is
discontinuous at the lowest charge current setting since
charge current accuracy suffers greatly if the inductor
current is discontinuous. Inductor current ripple (ΔIL) can
be computed using the following equation:
∆IL=VBAT •1– VBAT
VSYS
⎛
⎝
⎜
⎞
⎠
⎟•1
L•fOSC
Since the lowest recommended charge current set-
ting is 500mA, inductor current will be discontinuous if
the ripple is more than twice that amount, i.e, 1A. For
V
SYS
=5V, V
BAT
=3.2V, f
OSC
=2.25MHz (buck mode),
and ΔIL=1A, the theoretical minimum inductor size to
avoid discontinuous operation can be computed by using
the above equation to be 0.5µH. To account for inaccura-
cies in the system and component values, the practical
low limit should be 1µH. Since the backup boost oper-
ates at half the frequency (1.125MHz), the inductor cur-
rent ripple with a 1µH inductor using the same equation
will be approximately 1A in backup mode. If this seems
excessive, inductors up to 2.2µH can be used to lower the
inductor current ripple.
The other considerations when choosing an inductor is
the maximum DC current (IDC) and the maximum DC
resistance (DCR) rating as shown in Table 3 below. The
chosen inductor should have a max IDC rating which is
greater than the current limit specification of the part in
order to prevent an inductor current runaway situation.
For the LTC4040, the maximum current that the inductor
can experience is approximately 8A in backup mode. It is
also important to keep the max DCR as low as possible
in order to minimize conduction loss and help improve
the converter’s efficiency.
Table 3. Recommended Inductors for the LTC4040
INDUCTOR
TYPE
L
(µH)
MAX
IDC
(A)
MAX
DCR
(MΩ)
SIZE IN mm
(L × W × H) MANUFACTURER
XAL-5020-122 1.2 8.3 20.5 5.68 × 5.68
× 2
Coilcraft
www.coilcraft.com
XAL-6030-122 1.2 10.8 7.5 6.76 × 6.76
× 3.1
Coilcraft
www.coilcraft.com
XAL-6020-132 1.3 9 15.4 6.76 × 6.76
× 2.1
Coilcraft
www.coilcraft.com
XAL-6030-182 1.8 14 10.52 6.76 × 6.76
× 3.1
Coilcraft
www.coilcraft.com
XAL-5030-222 2.2 9.2 14.5 5.3 × 5.5
× 3.1
Coilcraft
www.coilcraft.com
XAL-6030-222 2.2 15.9 13.97 6.38 × 6.58
× 3.1
Coilcraft
www.coilcraft.com
CHOOSING VSYS CAPACITOR
The worst-case delay for the backup boost converter to
meet the system load demand can happen if the PFI input
falls below the externally set threshold at a time when the
buck charger is charging at the highest setting of 2.5A
applicaTions inForMaTion
LTC4040
21
4040fb
For more information www.linear.com/LTC4040
and the system load is also very high, e.g., 2.5A. Under
this scenario, as soon as the part initiates the backup
mode, the inductor current will have to reverse from 2.5A
(from SW to BAT) to as high as the boost current limit
of approximately 6.5A (from BAT to SW). That is a 9A
current change in the inductor with a slope of VBAT/L. At
a low battery voltage of 3.2V, this might take almost 3µs
even with a 1µH inductor. During this transition, C
SYS
, the
capacitor on the VSYS pin, will have to deliver the shortfall
until the inductor current is caught up with the system
load demand, and the capacitor will deplete according to
the following equation:
CSYS =ILOAD •
∆t
∆V
The size of the capacitor should be big enough to hold the
system voltage, VSYS, up above the reset threshold during
this transition. For a system load ILOAD = 2.5A, transition
time ∆t = 3µs, if the maximum droop ∆V allowed in the
system output is 100mV, the required capacitance at the
VSYS pin should be at least 75µF.
The other consideration for choosing VSYS capacitor size
is the maximum acceptable output voltage ripple during
steady-state backup boost operation. For a given duty
cycle of D and load of ILOAD, the output ripple VRIP of a
boost converter is calculated using the following equation:
VRIP =
I
LOAD
C
SYS
•D•
1
f
OSC
If the maximum allowable ripple is 20mV under 2.5A
steady-state load while boosting from 3.2V to 5V
(D = 36%), the required capacitance at VSYS is calcu-
lated to be at least 40µF using the above equation. Please
refer to Table 4 for recommended ceramic capacitor
manufacturers.
Table 4. Recommended Ceramic Capacitor Manufacturers
AVX www.avxcorp.com
Murata www.murata.com
Taiyo Yuden www.t-yuden.com
Vishay Siliconix www.vishay.com
TDK www.tdk.com
BATTERY CHARGER STABILITY CONSIDERATIONS
The LTC4040’s switching battery charger contains three
control loops: constant-voltage, constant-current, and
input current limit loop, all of which are internally com-
pensated. However, various external conditions like load
and component values may interfere with the internal
compensation and cause instability. For example, the con-
stant-voltage loop may become unstable due to reduced
phase margin if more than 100µF capacitance is added in
parallel with the actual battery at the BAT pin.
In constant-current mode, the PROG pin is in the feedback
loop rather than the BAT pin. Because of the additional
pole created by any PROG pin capacitance, capacitance on
this pin must be kept to a minimum. For the constant-cur-
rent loop to be stable, the pole frequency at the PROG pin
should be kept above 1MHz. Therefore, if the PROG pin
has a parasitic capacitance, CPROG, the following equa-
tion should be used to calculate the maximum resistance
value for RPROG:
RPROG ≤
1
2π•1MHz •CPROG
Alternatively, for RPROG = 4k (500mA setting), the maxi-
mum allowable capacitance on the PROG pin is 40pF. If
any measuring device is attached to the PROG pin for
monitoring the charge current, a 1M isolation resistor
should be inserted between the PROG pin and the device.
BACKUP BOOST STABILITY CONSIDERATIONS
The LTC4040’s backup boost converter is internally com-
pensated. However, system capacitance less than 100µF
or over 1000µF will adversely affect the phase margin and
hence the stability of the converter.
Also, if the right-half-plane (RHP) zero moves down in
frequency due to external load conditions and the choice
of the inductor value, that may also reduce the phase
margin and cause instability. If the output power is POUT,
inductor value is L, efficiency is η and the input to the
applicaTions inForMaTion
LTC4040
22
4040fb
For more information www.linear.com/LTC4040
applicaTions inForMaTion
boost converter is VBAT, the RHP zero frequency can be
expressed as follows:
fRHP =VBAT
( )
2
2•π•L•POUT
•η
For the LTC4040’s backup boost to be able to supply
12.5W of output power (2.5A at 5V) from a 3.2V bat-
tery, the maximum inductor size should not exceed 2.2µH
because of the RHP zero consideration. Also, too much
lead resistance between the battery and the BAT pin can
lower the effective input voltage of the boost converter
causing the RHP zero to shift downward and cause insta-
bility. This is why it is important to minimize the lead
resistance and place the battery as close to the BAT pin
as possible.
ALTERNATE NTC THERMISTORS AND BIASING
The hot and cold trip points may be adjusted using a
different type of thermistor, or a different RBIAS resistor,
or by adding a desensitizing resistor RADJ as shown in
Figure2, or by a combination of these measures. For
example, by increasing RBIAS to 12.4k from the default
value of 10k, with the same Vishay Curve 2 thermistor,
the cold trip point moves down to –5°C, and the hot trip
point moves down to 34°C. If a Vishay Curve1 thermis-
tor with ß25/85=3950K and resistor of 100k at 25°C is
used, a 1% R
BIAS
resistor of 118k and a 1% R
ADJ
resistor
of 12.1k results in a cold trip point of 0°C, and a hot trip
point of 39°C.
+
–
1.7% VIN
IGNORE NTC
+
–
29% VIN
TOO HOT
+
–
74% VIN
TOO COLD
LTC4040
NTC
RBIAS
RADJ
OPT
RNTC Li-Ion
4040 F01
BAT
VIN
+
Figure2. NTC Connections
PCB LAYOUT CONSIDERATIONS
Since the LTC4040 includes a high-current high-frequency
switching converter, the following guidelines should
be used during printed circuit board (PCB) layout in
order to achieve optimum performance and minimum
electromagnetic interference (EMI).
1. Even though the converter can operate in both step-
down (buck) and step-up (boost) mode, there is only
one hot-loop containing high-frequency switching
currents. The simplified diagram in Figure3 can be
used to explain the hot-loop in the LTC4040 switching
converter. Current follows the blue loop when switch
S2 (NMOS) is closed and the red loop when switch
S1 (PMOS) is closed. So it is evident that the current
in the CBAT capacitor is continuous whereas the CSYS
current is discontinuous forming a hot loop with V
SYS
pins and GND as indicated by the green loop. Since
the amount of EMI is directly proportional to the area
of this loop, the VSYS capacitor, prioritized over all
else, should be placed as close to the VSYS pins as
possible and the ground side of the capacitor should
return to the ground plane through an array of vias.
+
V
BAT HOT LOOP
CBAT
4040 F03
CSYS
S2
S1
L1
VSYS
Figure3. Hot-Loop Illustration for the LTC4040 Switching Converter
2. To minimize parasitic inductance, the ground plane
should be as close as possible to the top plane of the
PC board (Layer 2). High frequency currents in the hot
loop tend to flow along a mirror path on the ground
plane which is directly beneath the incident path on
the top plane of the board as illustrated in Figure4. If
there are slits or cuts or drill-holes in this mirror path
on the ground plane due to other traces, the current
will be forced to go around the slits. When high fre-
quency currents are not allowed to flow back through
their natural least-area path, excessive voltage will
LTC4040
23
4040fb
For more information www.linear.com/LTC4040
Typical applicaTion
+
324k
2.2µH
VSYS
PROGBSTOFF GNDCHGOFF F2F1F0
IGATE
LTC4040
VIN CLN
1690k
MN2
5V
RS
12mΩ
VOUT
5V
10µF
100µF
47µF
4.7µF 0.1µF
SYSTEM
LOAD
BSTFB
RSTFB
SW
BAT
NTC
NTC
VSYS
2k
Li-Ion
4.1V
4040 TA02
VOUT
OVSNS
PFI
FAULT
PFO
RST
CHRG
CLPROG
178k
60.4k
243k
L1: COILCRAFT XAL-5030-222
MN2: VISHAY/SILICONIX SIR424DP-T1-GE3
18.2k
4.7µH
1M
10nF
10pF
1µF
BST
VIN
12V VIN
EN/UV
PG
SYNC
TR/SS
INTVCC
PGND
LT8610
GNDRT
SW
BIAS
FB
5V Backup System with 12V Buck for Automotive Application
(Charge Current Setting: 1A, Input Current Limit Setting: 2A)
build up and radiated emissions will occur. So every
effort should be made to keep the hot-loop current
path as unbroken as possible.
3586 F04
Figure4. High Frequency Ground Currents Follow Their Incident Path.
Slices in the Ground Plane Cause High Voltage and Increased EMI
3. The other important components that need to be
placed close to the pins are the CBAT capacitor and
the inductor L1. Even though the current through
these components is continuous, they can change
very abruptly due to a sudden change in load demand.
Also, their traces should be wide enough to handle
currents as high as the NMOS current limit (typ. 6.5A)
in backup boost mode.
4. Locate the VSYS dividers for BSTFB and RSTFB near
the part but away from the switching components.
Kelvin the top of the resistor dividers to the positive
terminal of CSYS. The bottom of the resistor dividers
should return to the ground plane away from the hot-
loop current path. The same is true for the PFI divider.
5. The exposed pad on the backside of the LTC4040
package must be securely soldered to the PC board
ground and also must have a group of vias con-
necting it to the ground plane for optimum thermal
performance. Also this is the only ground pin in the
package, and it serves as the return path for both the
control circuitry and the switching converter.
6. The IGATE pin for controlling the gates of the external
pass transistors has extremely limited drive current.
Care must be taken to minimize leakage to adjacent
PC board traces. To minimize leakage, the trace can
be guarded on the PC board by surrounding it with
VSYS connected metal.
applicaTions inForMaTion
LTC4040
24
4040fb
For more information www.linear.com/LTC4040
package DescripTion
Please refer to http://www.linear.com/product/LTC4040#packaging for the most recent package drawings.
UFD Package
24-Lead Plastic QFN (4mm × 5mm)
(Reference LTC DWG # 05-08-1696 Rev A)
4.00 ±0.10
(2 SIDES)
5.00 ±0.10
(2 SIDES)
NOTE:
1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WXXX-X).
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
23 24
1
2
BOTTOM VIEW—EXPOSED PAD
0.75 ±0.05 R = 0.115
TYP
R = 0.05 TYP PIN 1 NOTCH
R = 0.20 OR C = 0.35
0.25 ±0.05
0.50 BSC
0.200 REF
0.00 – 0.05
(UFD24) QFN 0506 REV A
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
0.70 ±0.05
0.25 ±0.05
0.50 BSC
2.65 ±0.05
2.00 REF
3.00 REF
4.10 ±0.05
5.50 ±0.05
3.10 ±0.05
4.50 ±0.05
PACKAGE OUTLINE
2.65 ±0.10
2.00 REF
3.00 REF
3.65 ±0.10
3.65 ±0.05
UFD Package
24-Lead Plastic QFN (4mm × 5mm)
(Reference LTC DWG # 05-08-1696 Rev A)
LTC4040
25
4040fb
For more information www.linear.com/LTC4040
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
revision hisTory
REV DATE DESCRIPTION PAGE NUMBER
A 07/15 Added new Applications section, Charge Voltage
Modified Figure 2
Re-assigned new figure numbers
18
22
22 – 23
B 08/17 Changed Maximum Boost Duty Cycle maximum limit. 4
LTC4040
26
4040fb
For more information www.linear.com/LTC4040
LINEAR TECHNOLOGY CORPORATION 2015
LT 0817 REV B • PRINTED IN USA
www.linear.com/LTC4040
relaTeD parTs
Typical applicaTion
5V Backup Application with OVP Protection and Non-Backed Up Load Option
(Charge Current Setting: 2.5A, Input Current Limit Setting: 4A)
+
324k
2.2µH
VSYS
PROGBSTOFF GNDCHGOFF F2F1F0
IGATE
LTC4040
VIN CLN
1690k
MN2
MN1 VSYS
4.35V TO 5V
RS
6mΩ
10µF
RBIAS
100µF
2.2µF
TO BACKED-UP
SYSTEM LOAD
TO NON-BACKED-UP
LOAD
BSTFB
RSTFB
4.35V TO 5V
INPUT SUPPLY
(PROTECTED
TO 40V)
SW
BAT
NTC
NTC
800Ω
Li-Ion
BATTERY
4.1V
4040 TA03
VIN
VSYS
OVSNS
PFI
FAULT
PFO
RST
CHRG
CLPROG
60.4k
178k
6.2k 1/4W
OVP OPT
L1: COILCRAFT XAL-5030-222
MN1: VISHAY/SILICONIX SiS488DN
MN2: VISHAY/SILICONIX SIR424DP-T1-GE3
VPWR
PART NUMBER DESCRIPTION COMMENTS
LTC3226 2-Cell Supercapacitor Charger with Backup PowerPath™
Controller
1x/2x Multimode Charge Pump Supercapacitor Charger, Internal 2A LDO
Backup Supply
LTC3350 High Current Supercapacitor Backup Controller and
System Monitor
High Efficiency Synchronous Step-Down CC-CV Charging of 1-4 Series
Supercapacitors
LTC3355 20V 1A Buck DC/DC with Integrated SCAP Charger and
Backup Regulator
1A Main Buck Regulator, 5A Boost Backup Regulator
LTC4089 USB Power Manager with High Voltage Switching
Charger
1.2A Charger for Li-Ion from 6V to 86V Supply
LTC4090 USB Power Manager with 2A High Voltage Bat-Track
Buck Regulator
2A Charger with Bat-Track for Li-Ion Batteries
LTC4110 Battery Backup System Manager Complete Manager for Li-Ion/Polymer, Lead Acid, NiMH/NiCd Batteries
and Supercapacitors
LTC4155/LTC4156 Dual Input Power Manager/3.5A Li-Ion Battery Charger
with I2C Control and USB OTG
3.5A Charge Current for Li-Ion/Polymer, LTC4156 for LiFePO4 Batteries
LTC4160 Switching Power Manager with USB On-The-Go and
Overvoltage Protection
1.2A Charge Current