Final Electrical Specifications
LTC1732-4/LTC1732-4.2
Lithium-Ion Linear
Battery Charger Controller
FEATURES
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DESCRIPTIO
October 2000
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Complete Linear Charger Controller for 1-Cell
Lithium-Ion Batteries
Preset Charge Voltage with 1% Accuracy
4.5V to 12V Input Voltage Range
Programmable Charge Current
C/10 Charge Current Detection Output
Programmable Charge Termination Timer
Small, Thin 10-Pin MSOP Package
Select Pin to Charge Either 4.1V or
4.2V Cells (LTC1732-4)
Automatic Sleep Mode When Input Supply
is Removed (Only 7µA Battery Drain)
Automatic Trickle Charge of Low Voltage Cells
Programmable for Constant-Current-Only Mode
Battery Insertion Detect and Automatic Charging
of Low-Battery Cell
Input Supply (Wall Adapter) Detection Output
4.05V Recharge Threshold for 4.2V Cells
(LTC1732-4.2)
3.8V Recharge Threshold for 4.1V or 4.2V Cells
(LTC1732-4)
The LTC
®
1732 is a complete constant-current/constant-
voltage linear charge controller for lithium-ion
(Li-Ion) batteries. Nickel-cadmium (NiCd) and nickel metal-
hydride (NiMH) batteries can also be charged with con-
stant current using external termination. Charge current
can be programmed with 7% (max) accuracy using exter-
nal sense and program resistors. An internal resistor
divider and precision reference set the final float voltage
with 1% accuracy. The SEL pin allows users to charge
either 4.1V or 4.2V cells.
When the input supply is removed, the LTC1732 automati-
cally enters a low current sleep mode, dropping the battery
drain current to 7µA. An internal comparator detects the
end-of-charge (C/10) condition while a programmable
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 LTC1732 begins a new charge cycle when a discharged
battery is connected to the charger or when the input power
is applied. In addition, if the battery remains connected to
the charger and the cell voltage drops below 3.8V for the
LTC1732-4 or below 4.05V for the LTC1732-4.2, a new
charge cycle will begin.
The LTC1732 is available in the 10-pin MSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIONS
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Cellular Phones
Handheld Computers
Charging Docks and Cradles
TYPICAL APPLICATION
Single Cell 4.2V Li-Ion Battery Charger
V
IN
= 6V
MBRM120T3
R2
1k
R1
1k
3
8
V
CC
2
SEL
SENSE
CHRG
DRV
9
7
R
SENSE
0.2Ω
Q1
Si9430DY
I
BAT
= 500mA
1µF
LTC1732-4
10
4
C
TIMER
0.1µF
ACPR
TIMER
BAT
PROG
1
6
R
PROG
*
19.6k
GND
5
10µF
+
4.2V
Li-Ion
CELL
1732 TA01
*SHUTDOWN INVOKED BY FLOATING THE PROG PIN
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.
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LTC1732-4/LTC1732-4.2
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
BAT
SEL
CHRG
TIMER
GND
1
2
3
4
5
10
9
8
7
6
ACPR
SENSE
V
CC
DRV
PROG
Input Supply Voltage (V
CC
) ................................... 13.2V
SENSE, DRV, BAT, SEL, TIMER, PROG,
CHRG, ACPR ......................................... – 0.3V to 13.2V
Operating Temperature Range (Note 2) .... – 40° to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC1732EMS-4
LTC1732EMS-4.2
MS10 PART MARKING
LTNJ
LTUA
MS10 PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 140°C,
θ
JA
= 180°C/W
Consult factory for Industrial and Military grade parts.
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)
LTC1732-4; 5V
≤
V
CC
≤
12V, V
SEL
= GND
LTC1732-4/LTC1732-4.2; 5V
≤
V
CC
≤
12V, V
SEL
= V
CC
R
PROG
= 19.6k, R
SENSE
= 0.2Ω
R
PROG
= 19.6k, R
SENSE
= 0.2Ω
R
PROG
= 97.6k, R
SENSE
= 0.2Ω
I
TRIKL
V
TRIKL
V
UV
∆V
UV
V
MSD
V
ASD
V
DIS
I
PROG
V
PROG
V
ACPR
I
CHRG
V
CHRG
V
SEL
Trickle Charge Current
Trickle Charge Threshold Voltage
V
CC
Undervoltage Lockout Voltage
V
CC
Undervoltage Lockout Hysteresis
Manual Shutdown Threshold Voltage
Automatic Shutdown Threshold Voltage
Voltage Mode Disable Threshold Voltage
PROG Pin Current
PROG Pin Voltage
ACPR Pin Output Low Voltage
CHRG Pin Weak Pull-Down Current
CHRG Pin Output Low Voltage
SEL Pin Threshold
PROG Pin Low to High
PROG Pin High to Low
(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
I
ACPR
= 5mA
V
CHRG
= 1V
I
CHRG
= 5mA
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
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q
q
MIN
4.5
TYP
1
1
7
MAX
12
3
3
20
4.141
4.242
535
585
140
110
2.55
4.5
UNITS
V
mA
mA
µA
V
V
mA
mA
mA
mA
V
V
mV
V
V
V
BAT
I
BAT
Regulated Output Voltage
Current Mode Charge Current
4.059
4.158
465
415
60
30
2.35
4.1
4.2
500
100
50
2.457
4.1
200
2.457
2.446
V
BAT
= 2V, R
PROG
= 19.6k, I
TRIKL
= (V
CC
– V
SENSE
)/0.2Ω
q
From Low to High
From Low to High
q
q
30
40
54
69
2.5
90
100
0.4
q
300
2.457
0.7
15
0.3
35
0.6
1.2
55
1.2
2
2
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mV
mV
V
µA
µA
V
V
µA
V
V
LTC1732-4/LTC1732-4.2
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
I
C/10
t
TIMER
V
RECHRG
PARAMETER
End of Charge Indication Current Level
TIMER Accuracy
Recharge Battery Voltage Threshold per Cell
CONDITIONS
R
PROG
= 19.6k, R
SENSE
= 0.2Ω
C
TIMER
= 0.1µF
V
BAT
from High to Low (LTC1732-4)
V
BAT
from High to Low (LTC1732-4.2)
3.72
3.95
q
ELECTRICAL CHARACTERISTICS
MIN
25
TYP
50
10
3.80
4.05
MAX
100
UNITS
mA
%
V
V
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC1732E 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.
PIN FUNCTIONS
BAT (Pin 1):
Battery Sense Input. A bypass capacitor of
10µF or more is required to keep the loop stable when the
battery is not connected. A precision internal resistor
divider on this pin sets the final float potential. The resistor
divider is disconnected in sleep mode to reduce the
current drain on the battery.
SEL (Pin 2):
4.1V/4.2V Battery Selection Input Pin. Ground-
ing this pin will set the output float voltage to 4.1V per cell,
while connecting to V
CC
will set the voltage to 4.2V per cell.
For the LTC1732-4.2, the SEL pin must be connected to
V
CC
.
CHRG (Pin 3):
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 more than 15ms,
the N-channel MOSFET turns off and a 35µA 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 4):
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 timer is disabled, the constant-
voltage mode is disabled and the chip will operate in
constant-current mode only. Shorting the TIMER pin to
GND will disable the internal timer function and the
C/10
function.
GND (Pin 5):
Ground.
PROG (Pin 6):
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 7):
Drive Output Pin for the P-Channel MOSFET
or PNP Transistor. The impedance is high at this pin,
therefore, a high gain PNP pass transistor should be used.
V
CC
(Pin 8):
Positive Input Supply Voltage. When V
BAT
is
within 54mV of V
CC
, the LTC1732 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 9):
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
)
ACPR (Pin 10):
Wall Adapter Present Output. When the
input voltage (wall adaptor) is applied to the LTC1732, this
pin is pulled to ground by an internal N-channel MOSFET
that is capable of sinking 5mA to drive an external LED.
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LTC1732-4/LTC1732-4.2
BLOCK DIAGRA
2
CHRG
C/10 STOP RECHRG
C/10
35µA
ACPR
SHDN
LOGIC
SLP
720Ω
3
OSCILLATOR
V
REF
COUNTER
10
ACPR
C3
+
–
+
A1
–
2.5µA
V
REF
2.457V
CHARGE
PROG
R
PROG
GND
5
BATTERY CURRENT I
BAT
= (2.457V • 800Ω)/(R
PROG
• R
SENSE
)
OPERATIO
The LTC1732 is a linear battery charger controller. The
charge current is programmed by the combination of a
program resistor (R
PROG
) from the PROG pin to ground
and a sense resistor (R
SENSE
) between the V
CC
and SENSE
pins. R
PROG
sets a program current through an internal
trimmed 800Ω resistor setting up a voltage drop from V
CC
to the input of the current amplifier (CA). The current
amplifier servos the gate of the external P-channel MOSFET
to force the same voltage drop across R
SENSE
which sets
the charge current. When the potential at the BAT pin
approaches the preset float voltage, the voltage amplifier
(VA) will start sinking current which shrinks the voltage
drop across R
SENSE
, thus reducing the charge current.
Charging begins when the potential at V
CC
pin rises above
the UVLO level and a program resistor is connected from
the PROG pin to ground. At the beginning of the charge
cycle, if the battery voltage is below 2.457V, the charger
goes into trickle charge mode. The trickle charge current
is 10% of the full-scale current. If the cell voltage stays low
for one quarter of the total charge time, the charge
sequence will terminate.
4
+
V
CC
VA
–
+
TIMER
LBO
C2
–
+
–
W
V
CC
7
+
C5
3.8V
–
R
SENSE
+
C1
80Ω
800Ω
SENSE
8
–
C4
+
–
+
–
CA
54mV
DRV
BAT
6
1
SEL
2
4
1732 BD
U
LTC1732-4/LTC1732-4.2
OPERATIO
The charger goes into the fast charge constant-current
mode after the voltage on the BAT pin rises above 2.457V.
In constant-current mode, the charge current is set by the
combination of R
SENSE
and R
PROG
.
When the battery approaches the final float voltage, the
charge current will begin to decrease. When the current
drops to 10% of the full-scale charge current, an internal
comparator will turn off the pull-down N-channel MOSFET
at the CHRG pin and connect a weak current source to
ground to indicate an end-of-charge (C/10) condition.
An external capacitor on the TIMER pin sets the total
charge time. After a time-out occurs, the charge cycle is
terminated and the CHRG pin is forced to a high imped-
ance state. To restart the charge cycle, simply remove the
input voltage and reapply it, or float the PROG pin momen-
tarily.
Replacing the battery while in the charge mode will cause
the timer to be reset if the cell voltage of the new battery
is below 3.8V. If the voltage is above 3.8V, the timer will
APPLICATIONS INFORMATION
Stop Charging
The charger is off when any of the following conditions exist:
the voltage at the V
CC
pin is below 4.1V, the voltage at the
V
CC
pin is higher than 4.1V but is less than 54mV above
V
BAT
, or the PROG pin is floating. The DRV pin will be pulled
to V
CC
and the internal resistor divider is disconnected to
reduce the current drain on the battery.
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in shutdown mode until V
CC
rises above 4.1V. To prevent oscillation around V
CC
=
4.1V, the UVLO circuit has built-in hysteresis.
Trickle Charge and Defective Battery Detection
At the beginning of the charging sequence, if the battery
voltage is below 2.457V, the charger goes into trickle
mode. The charge current is dropped to 10% of the full-
scale current. If the low cell voltage persists for one
quarter of the total charging time, the battery is considered
defective, the charging will be terminated and the CHRG
pin output is forced to a high impedance state.
Shutdown
The LTC1732 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. The DRV pin will then be pulled up to V
CC
and turn
off the external P-channel MOSFET. The internal timer is
reset in the shutdown mode.
Programming Charge Current
The formula for the battery charge current (see Block
Diagram) is:
I
BAT
= (I
PROG
)(800Ω/R
SENSE
)
= (2.457V/R
PROG
)(800Ω/R
SENSE
)
where R
PROG
is the total resistance from the PROG pin to
ground.
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continue for the remaining charge time. In the case when
a time out has occurred, a new battery with the cell voltage
of less than 3.8V can be inserted and charged automati-
cally with the full programmed charge time.
For batteries like lithium-ion that require accurate final
float potential, the internal 2.457V reference, voltage am-
plifier and the resistor divider provide regulation with
±1%
(max) accuracy. For NiMH and NiCd batteries, the LTC1732
can be turned into a current source by pulling the TIMER
pin to V
CC
. When in the constant-current only mode, the
voltage amplifier, timer,
C/10
comparator and the trickle
charge function are all disabled.
The charger can be shut down by floating the PROG pin.
An internal current source will pull this pin high and clamp
it at 3.5V.
When the input voltage is not present, the charger goes
into a sleep mode, dropping I
CC
to 7µA. This greatly
reduces the current drain on the battery and increases the
standby time.
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