LTC1731-4.1/LTC1731-4.2
Single Cell Lithium-Ion Linear
Battery Charger Controllers
FEATURES
s
s
s
s
s
s
s
DESCRIPTIO
s
s
Complete Linear Charger Controller for
1-Cell Lithium-Ion Batteries
1% Voltage Accuracy
Programmable Charge Current
C/10 Charge Current Detection Output
Programmable Charge Termination Timer
Space Saving 8-Pin MSOP Package
Automatic Sleep Mode When Input Supply
is Removed (7µA Battery Drain)
Automatic Trickle Charging of Low Voltage Cells
Programmable for Constant-Current-Only Mode
The LTC
®
1731 is a complete constant-current/constant-
voltage linear charger controller for single cell lithium-ion
batteries. Nickel-cadmium (NiCd) and nickel-metal-hy-
dride (NiMH) batteries can also be charged with constant
current using external termination. The external sense
resistor sets the charge current with 5% accuracy. An
internal resistor divider and precision reference set the
final float potential with
±1%
accuracy. The output float
voltage is set internally to 4.1V (LTC1731-4.1) or 4.2V
(LTC1731-4.2).
When the input supply is removed, the LTC1731 automati-
cally enters a low current sleep mode, dropping the battery
drain current to typically 7µA. An internal comparator
detects the end-of-charge (C/10) condition while a pro-
grammable timer, using an external capacitor, sets the
total charge time. Fully discharged cells are automatically
trickle charged at 10% of the programmed current until
cell voltage exceeds 2.457V.
The LTC1731 is available in the 8-pin MSOP and SO
packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Cellular Phones
Handheld Computers
Charging Docks and Cradles
Programmable Current Source
TYPICAL APPLICATIO
500mA Li-Ion Battery Charger
V
IN
= 6V
MBRM120T3
7
1k
CHARGE
STATUS
V
CC
SENSE
2
CHRG
DRV
8
6
R
SENSE
0.2Ω
Q1
Si9430DY
I
BAT
= 500mA
LTC1731-4.2
3
C
TIMER
0.1µF
TIMER
BAT
PROG
GND
4
1
5
R
PROG
*
19.6k
+
Li-ION
CELL
*SHUTDOWN INVOKED BY FLOATING THE PROG PIN
U
1µF
10µF
1731 TA01
U
U
1
LTC1731-4.1/LTC1731-4.2
ABSOLUTE
MAXIMUM
RATINGS
Input Supply Voltage (V
CC
) ................................... 13.2V
Input Voltage (SENSE, DRV, BAT,
TIMER, PROG) .................................. – 0.3V to 13.2V
Output Voltage (CHRG) ......................... – 0.3V to 13.2V
PACKAGE/ORDER INFORMATION
TOP VIEW
BAT
CHRG
TIMER
GND
1
2
3
4
8
7
6
5
SENSE
V
CC
DRV
PROG
ORDER PART
NUMBER
BAT 1
LTC1731EMS8-4.1
LTC1731EMS8-4.2
MS8 PART MARKING
LTJK
LTKQ
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 150°C,
θ
JA
= 200°C/W
Consult factory for parts specified with wider operating temperature ranges.
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 6V unless otherwise noted.
SYMBOL
V
CC
I
CC
PARAMETER
Input Supply Voltage
Input Supply Current
Charger On, Current Mode
Shutdown Mode
Sleep Mode (Battery Drain Current)
LTC1731-4.1 (5V
≤
V
CC
≤
12V)
LTC1731-4.2 (5V
≤
V
CC
≤
12V)
R
PROG
= 19.6k, R
SENSE
= 0.2Ω
R
PROG
= 19.6k, R
SENSE
= 0.2Ω
R
PROG
= 97.6k, R
SENSE
= 0.2Ω
V
BAT
= 2V, R
PROG
= 19.6k, I
TRIKL
= (V
CC
– V
SENSE
)/0.2Ω
From Low to High
From Low to High
PROG Pin Low to High
PROG Pin High to Low
CONDITIONS
q
q
q
q
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
V
BAT
I
BAT
Regulated Output Voltage
Current Mode Charge Current
I
TRIKL
V
TRIKL
V
UV
∆V
UV
V
MSD
Trickle Charge Current
Trickle Charge Threshold Voltage
V
CC
Undervoltage Lockout Voltage
V
CC
Undervoltage Lockout Hysteresis
Manual Shutdown Threshold Voltage
2
U
U
W
W W
U
W
(Note 1)
Operating Temperature Range (Note 2) .....– 40° to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
8
7
6
5
SENSE
V
CC
DRV
PROG
ORDER PART
NUMBER
LTC1731ES8-4.1
LTC1731ES8-4.2
S8 PART MARKING
173141
173142
CHRG 2
TIMER 3
GND 4
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 125°C/W
MIN
4.5
TYP
1
1
7
MAX
12
3
2
20
4.141
4.242
535
585
130
100
2.55
4.5
UNITS
V
mA
mA
µA
V
V
mA
mA
mA
mA
V
V
mV
V
V
4.059
4.158
465
415
70
30
2.35
4.1
4.2
500
100
50
2.457
4.1
200
2.457
2.446
LTC1731-4.1/LTC1731-4.2
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 6V unless otherwise noted.
SYMBOL
V
ASD
V
DIS
I
PROG
V
PROG
I
CHRG
V
CHRG
I
C/10
t
TIMER
V
CLAMP
PARAMETER
Automatic Shutdown Threshold Voltage
Voltage Mode Disable Threshold Voltage
PROG Pin Current
PROG Pin Load Regulation
PROG Pin Voltage
CHRG Pin Weak Pull-Down Current
CHRG Pin Output Low Voltage
End of Charge Indication Current Level
TIMER Accuracy
DRV Pin Clamp Voltage
CONDITIONS
(V
CC
– V
BAT
) High to Low
(V
CC
– V
BAT
) Low to High
V
DIS
= V
CC
– V
TIMER
Internal Pull-Up Current, No R
PROG
PROG Pin Source Current,
∆V
PROG
≤
5mV
R
PROG
=19.6k
V
CHRG
= 1V
I
CHRG
= 5mA
R
PROG
= 19.6k, R
SENSE
= 0.2Ω
C
TIMER
= 0.1µF
V
CLAMP
= V
CC
– V
DRV
, I
DRIVE
= 50µA
q
q
q
ELECTRICAL CHARACTERISTICS
MIN
30
40
TYP
54
69
2.5
MAX
90
100
0.4
UNITS
mV
mV
V
µA
µA
V
300
2.457
50
25
100
0.6
50
10
6.5
150
1.2
100
µA
V
mA
%
V
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC1731E 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. Guaranteed I grade parts are available,
consult factory.
TYPICAL PERFOR A CE CHARACTERISTICS
Trickle Charge Current
vs Input Supply
60
R
PROG
= 19.6k
R
SENSE
= 0.2Ω
V
BAT
= 2V
T
A
= 25°C
V
PROG
(V)
55
I
TRKL
(mA)
50
2.460
t
TIMER
(%)
45
40
4
6
8
V
CC
(V)
10
U W
1731 G01
Program Pin Voltage
vs Temperature
2.470
V
CC
= 6V
R
PROG
= 19.6k
110
Timer Accuracy vs Temperature
V
CC
= 6V
C
TIMER
= 0.1µF
2.465
105
100
2.455
95
12
2.450
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1731 G02
90
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1731 G03
3
LTC1731-4.1/LTC1731-4.2
TYPICAL PERFOR A CE CHARACTERISTICS
Trickle Charge Threshold Voltage
vs Temperature
2.470
V
CC
= 6V
110
2.465
t
TIMER
(%)
V
TRKL
(V)
2.460
100
I
TRKL
(mA)
2.455
2.450
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1731 G04
Battery Charge Current
vs Temperature
540
R
PROG
= 19.6k
530 R
SENSE
= 0.2Ω
V
BAT
= 3V
520 V
CC
= 6V
2.480
I
BAT
(mA)
V
TRKL
(V)
510
500
490
480
470
460
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1731 G07
Program Pin Voltage
vs Input Supply
2.480
R
PROG
= 19.6k
V
BAT
= 3V
2.475
T
A
= 25°C
2.470
V
PROG
(V)
2.460
2.455
2.450
2.445
2.440
4
6
8
V
CC
(V)
1731 G09
I
BAT
(mA)
2.465
4
U W
Timer Accuracy vs Input Supply
V
BAT
= 3V
C
TIMER
= 0.1µF
T
A
= 25°C
60
Trickle Charge Current
vs Temperature
R
PROG
= 19.6k
R
SENSE
= 0.2Ω
V
BAT
= 2V
V
CC
= 6V
55
105
50
95
45
90
4
6
8
V
CC
(V)
10
12
1731 G05
40
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1731 G06
Trickle Charge Threshold Voltage
vs Input Supply
R
PROG
= 19.6k
2.475 T
A
= 25°C
2.470
2.465
2.460
2.455
2.450
2.445
2.440
4
6
8
V
CC
(V)
1731 G08
10
12
Battery Charge Current
vs Input Supply
520
R
PROG
= 19.6k
R
SENSE
= 0.2Ω
515
V
BAT
= 3V
510 T
A
= 25°C
505
500
495
490
485
10
12
480
4
6
8
V
CC
(V)
1731 G10
10
12
LTC1731-4.1/LTC1731-4.2
PIN FUNCTIONS
BAT (Pin 1):
Battery Sense Input. A bypass capacitor of at
least 10µF is required to keep the loop stable when the
battery is not connected. A precision internal resistor
divider sets the final float potential on this pin. The resistor
divider is disconnected in sleep mode.
CHRG (Pin 2):
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 to 10% of the full-scale current for at least 0.32
seconds, the N-channel MOSFET turns off and a 100µA
current source is connected from the CHRG pin to GND.
When the timer runs out or the input supply is removed,
the current source will be disconnected and the CHRG pin
is forced into a high impedance state.
TIMER (Pin 3):
Timer Capacitor and Constant-Voltage
Mode Disable Input Pin. The timer period is set by placing
a capacitor, C
TIMER
, to GND. The timer period is t
TIMER
=
(C
TIMER
• 3 hours)/(0.1µF). When the TIMER pin is
connected to V
CC
, the constant-voltage mode and the
timer are disabled, the chip will operate in constant-
current mode only. Short the TIMER pin to GND to disable
the internal timer function and the
C/10
function.
GND (Pin 4):
Ground Connection.
PROG (Pin 5):
Charge Current Program and Shutdown
Input Pin. The charge current is programmed by connect-
ing a resistor, R
PROG
to ground. The charge current is I
BAT
= (V
PROG
• 800Ω)/(R
PROG
• R
SENSE
). The IC can be forced
into shutdown by floating the PROG pin. An internal 2.5µA
current source will pull the pin above the shutdown
threshold voltage when the program resistor (R
PROG
) is
disconnected.
DRV (Pin 6):
Drive Output Pin for the P-Channel MOSFET
or PNP Transistor. The impedance is high at this pin,
therefore, a high beta PNP pass transistor should be used.
The DRV pin is internally clamped to 6.5V below V
CC
.
V
CC
(Pin 7):
Positive Input Supply Voltage. When V
BAT
is
within 54mV of V
CC
, the LTC1731 is forced into sleep
mode, dropping I
CC
to 7µA. V
CC
ranges from 4.5V to 12V.
Bypass this pin with a 1µF capacitor.
SENSE (Pin 8):
Current Sense Input. A sense resistor,
R
SENSE
, must be connected from V
CC
to the SENSE pin.
This resistor is chosen using the following equation:
R
SENSE
= (V
PROG
• 800Ω)/(R
PROG
• I
BAT
)
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