LTC1731-8.2/LTC1731-8.4
Lithium-Ion Linear
Battery Charger Controller
FEATURES
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DESCRIPTIO
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Complete Linear Charger Controller for
2-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 (15µA Battery Drain)
Automatic Trickle Charging of Low Voltage Cells
Programmable for Constant-Current-Only Mode
The LTC
®
1731-8.2/LTC1731-8.4 are complete constant-
current/constant-voltage linear charger controllers for 2-
cell lithium-ion (Li-Ion)batteries. Nickel-cadmium (NiCd)
and nickel-metal-hydride (NiMH) batteries can also be
charged with constant current using external termina-
tion. The external sense resistor sets the charge current
with 7% accuracy. An internal resistor divider and preci-
sion reference set the final float potential with 1% accu-
racy. The output float voltages are set internally to 8.2V
(LTC1731-8.2) or 8.4V (LTC1731-8.4).
When the input supply is removed, the LTC1731-8.2/
LTC1731-8.4 automatically enter a low current sleep mode,
dropping the battery drain current to typically 15µA. An
internal comparator detects the end-of-charge (C/10) con-
dition while a programmable timer, using an external
capacitor, sets the total charge time. Fully discharged cells
are automatically trickle charged at 10% of the pro-
grammed current until battery voltage exceeds 4.95V.
The LTC1731-8.2/LTC1731-8.4 are available in the 8-pin
MSOP and SO packages. For 1-cell Li-Ion battery charg-
ing, see the LTC1731-4.1 and LTC1731-4.2 data sheets.
APPLICATIO S
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Cellular Phones
Handheld Computers
Charging Docks and Cradles
Programmable Current Source
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
400mA Li-Ion Charger
V
IN
= 9V
MBRM120T3
Typical Li-Ion Charge Cycle
CONSTANT
CURRENT
CONSTANT
VOLTAGE
BATTERY VOLTAGE
400
300
CHARGE CURRENT
200
100
10µF
0
1731 TA01
CHARGE CURRENT (mA)
7
2k
CHARGE
STATUS
V
CC
SENSE
2
CHRG
DRV
8
6
R
SENSE
0.2Ω
Q1
Si9430DY
I
BAT
= 400mA
1µF
LTC1731-8.4
3
C
TIMER
0.1µF
TIMER
BAT
PROG
GND
4
1
5
R
PROG
*
19.6k
+
2-CELL
Li-ION
0
0.5
*SHUTDOWN INVOKED BY FLOATING THE PROG PIN
U
9
U
U
BATTERY VOLTAGE(V)
400mA HR BATTERY
8
CHRG
LED OFF
7
TIMER
STOPS
6
3.0
2.0
1.5
1.0
TIME (HOURS)
2.5
1731 TA01b
sn1731 17318fs
1
LTC1731-8.2/LTC1731-8.4
ABSOLUTE
MAXIMUM
RATINGS
Input Supply Voltage (V
CC
) ................................... 13.2V
SENSE, DRV, BAT, TIMER, PROG ............ – 0.3V to V
CC
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
LTC1731EMS8-8.2
LTC1731EMS8-8.4
MS8 PART MARKING
LTSW
LTPE
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 150°C,
θ
JA
= 200°C/W
Consult LTC Marketing 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
= 9V 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)
LTC1731-8.2 (9V
≤
V
CC
≤
12V)
LTC1731-8.4 (9V
≤
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
= 4V, R
PROG
= 19.6k, I
TRIKL
= (V
CC
– V
SENSE
)/0.2Ω
BAT Rising
V
CC
Rising
V
CC
Falling
PROG Pin Rising
PROG Pin Falling
V
DRV
= V
CC
– 2V
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
I
DRV
Trickle Charge Current
Trickle Charge Threshold Voltage
V
CC
Undervoltage Lockout Voltage
V
CC
Undervoltage Lockout Hysteresis
Manual Shutdown Threshold Voltage
Drive Pin Current
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
LTC1731ES8-8.2
LTC1731ES8-8.4
S8 PART MARKING
173182
173184
CHRG 2
TIMER 3
GND 4
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 125°C/W
MIN
8.8
TYP
1
1
15
MAX
12
3
2
30
8.282
8.484
535
585
130
100
5.1
8.8
UNITS
V
mA
mA
µA
V
V
mA
mA
mA
mA
V
V
mV
V
V
µA
8.118
8.316
465
415
70
30
4.7
8.2
8.4
500
500
100
50
4.95
8.2
200
2.457
2.446
26
sn1731 17318fs
LTC1731-8.2/LTC1731-8.4
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 9V 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
) Falling
(V
CC
– V
BAT
) Rising
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
= 0.01µF
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-8.2/LTC1731E-8.4 are 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. Consult
factory for I grade parts.
TYPICAL PERFOR A CE CHARACTERISTICS
Trickle Charge Current
vs V
CC
60
R
PROG
= 19.6K
R
SENSE
= 0.2Ω
V
BAT
= 4V
T
A
= 25°
60
55
I
TRKL
(mA)
I
TRKL
(mA)
50
50
V
TRKL
(V)
45
40
9
10
V
CC
(V)
11
U W
1731 G01
Trickle Charge Current
vs Temperature
R
PROG
= 19.6K
R
SENSE
= 0.2Ω
V
BAT
= 4V
V
CC
= 9V
Trickle Charge Threshold Voltage
vs V
CC
4.96
4.95
4.94
4.93
4.92
4.91
R
PROG
= 19.6K
T
A
= 25°
55
45
4.90
4.89
12
40
–50 –25
0
25
50
75
100
125
4.88
9
10
V
CC
(V)
11
12
1731 G08
TEMPERATURE (°C)
1731 G06
sn1731 17318fs
3
LTC1731-8.2/LTC1731-8.4
TYPICAL PERFOR A CE CHARACTERISTICS
Trickle Charge Threshold Voltage
vs Temperature
4.94
V
CC
= 9V
110
4.93
t
TIMER
(%)
4.92
t
TIMER
(%)
V
TRKL
(V)
4.91
4.90
–50 –25
0
25
50
75
TEMPERATURE (°C)
1731 G03
Battery Charge Current
vs V
CC
520
R
PROG
= 19.6K
R
SENSE
= 0.2Ω
V
BAT
= 6V
T
A
= 25°
540
530
520
510
500
V
PROG
(V)
I
BAT
(mA)
I
BAT
(mA)
490
480
9
10
V
CC
(V)
11
V
PROG
(V)
4
U W
100
Timer Accuracy vs V
CC
C
TIMER
= 0.1µF
V
BAT
= 6V
T
A
= 25°
110
Timer Accuracy vs Temperature
C
TIMER
= 0.1µF
V
CC
= 9V
105
105
100
100
95
95
125
90
9
10
V
CC
(V)
11
12
1731 G05
90
–50 –25
0
25
50
75
100
125
TEMPERATURE (°C)
1731 G04
Battery Charge Current
vs Temperature
R
PROG
= 19.6K
R
SENSE
= 0.2Ω
V
BAT
= 6V
V
CC
= 9V
Program Pin Voltage
vs V
CC
2.48
R
PROG
= 19.6K
V
BAT
= 6V
T
A
= 25°
2.47
510
500
490
480
470
2.46
2.45
12
1731 G09
460
–50 –25
2.44
0
25
50
75
100
125
TEMPERATURE (°C)
1731 G07
9
10
V
CC
(V)
11
12
1731 G10
Program Pin Voltage
vs Temperature
2.470
R
PROG
= 19.6k
V
CC
= 9V
2.465
2.460
2.455
2.450
–50 –25
0
25
50
75
100
125
TEMPERATURE (°C)
1731 G02
sn1731 17318fs
LTC1731-8.2/LTC1731-8.4
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 resistive
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. A capacitor C
TIMER
connected
from this pin to ground sets a 30 hour/µF time period for
charge termination. When the TIMER pin is connected to
V
CC
, the constant-voltage mode and the timer is disabled
and the IC will operate in constant-current mode only.
Short the TIMER pin to GND to disable the internal timer
and the
C/10
functions.
GND (Pin 4):
Ground.
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 and allowing the
internal 2.5µA current source to pull the pin above the
2.457V shutdown threshold voltage.
DRV (Pin 6):
Drive Output Pin for the P-Channel MOSFET
or PNP Transistor. If a PNP transistor is used, it must have
high gain (see Applications Information section). The DRV
pin is internally clamped to 6.5V below V
CC
.
V
CC
(Pin 7):
Input Supply Voltage. V
CC
ranges from 8.8V
to 12V when charging. If V
CC
drops below V
BAT
+ 54mV,
for example when the input supply is disconnected, then
the IC enters sleep mode with I
CC
< 30µA. Bypass this pin
with a 1µF capacitor.
SENSE (Pin 8):
Current Sense Input. Connect this pin to
the sense resistor. Choose the resistor value using the
following equation:
R
SENSE
= (V
PROG
• 800Ω)/(R
PROG
• I
BAT
)
U
U
U
sn1731 17318fs
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