1
LTC1732-4/LTC1732-4.2
APPLICATIO S
U
DESCRIPTIO
U
FEATURES
TYPICAL APPLICATIO
U
Lithium-Ion Linear
Battery Charger Controller
The LTC
®
1732 is a complete constant-current/constant-
voltage linear charger 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 automatically begin.
The LTC1732 is available in the 10-pin MSOP package.
■
Complete Linear Charger Controller for 1-Cell
Lithium-Ion Batteries
■
Preset Charge Voltage with 1% Accuracy
■
Programmable Charge Current
■
C/10 Charge Current Detection Output
■
Programmable Charge Termination Timer
■
Small, Thin 10-Pin MSOP Package
■
Select Pin Charges 4.1V or 4.2V Cells (LTC1732-4)
■
Input Supply (Wall Adapter) Detection Output
■
4.5V to 12V Input Voltage Range
■
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
■
4.05V Recharge Threshold for 4.2V Cells
(LTC1732-4.2)
■
3.8V Recharge Threshold for 4.1V or 4.2V Cells
(LTC1732-4)
■
Cellular Phones
■
Handheld Computers
■
Charging Docks and Cradles
, LTC and LT are registered trademarks of Linear Technology Corporation.
Single Cell 4.2V Li-Ion Battery Charger
VCC
VIN = 6V
SENSE
DRV
R2
1k
R1
1k
RSENSE
0.2Ω
RPROG*
19.6k
4.2V
Li-Ion
CELL
LTC1732-4
*SHUTDOWN INVOKED BY FLOATING THE PROG PIN
BAT
CHRG
9
82
MBRM120T3
10µF
1732 TA01
1µF
IBAT = 500mA
CTIMER
0.1µF
Q1
Si9430DY
7
1
6
5
+
3
10
4ACPR
TIMER PROG
GND
SEL
2
LTC1732-4/LTC1732-4.2
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
CC
Input Supply Voltage ●4.5 12 V
I
CC
Input Supply Current Charger On, Current Mode ●13 mA
Shutdown Mode ●13 mA
Sleep Mode (Battery Drain Current) 7 20 µA
V
BAT
Regulated Output Voltage LTC1732-4; 5V ≤ V
CC
≤ 12V, V
SEL
= GND ●4.059 4.1 4.141 V
LTC1732-4/LTC1732-4.2; 5V ≤ V
CC
≤ 12V, V
SEL
= V
CC
●4.158 4.2 4.242 V
I
BAT
Current Mode Charge Current R
PROG
= 19.6k, R
SENSE
= 0.2Ω465 500 535 mA
R
PROG
= 19.6k, R
SENSE
= 0.2Ω●415 585 mA
R
PROG
= 97.6k, R
SENSE
= 0.2Ω60 100 140 mA
I
TRIKL
Trickle Charge Current V
BAT
= 2V, R
PROG
= 19.6k, I
TRIKL
= (V
CC
– V
SENSE
)/0.2Ω●30 50 110 mA
V
TRIKL
Trickle Charge Threshold Voltage From Low to High ●2.35 2.457 2.55 V
V
UV
V
CC
Undervoltage Lockout Voltage From Low to High ●4.1 4.5 V
∆V
UV
V
CC
Undervoltage Lockout Hysteresis 200 mV
V
MSD
Manual Shutdown Threshold Voltage PROG Pin Low to High 2.457 V
PROG Pin High to Low 2.446 V
V
ASD
Automatic Shutdown Threshold Voltage (V
CC
– V
BAT
) High to Low 30 54 90 mV
(V
CC
– V
BAT
) Low to High 40 69 100 mV
V
DIS
Voltage Mode Disable Threshold Voltage V
DIS
= V
CC
– V
TIMER
0.4 V
I
PROG
PROG Pin Current Internal Pull-Up Current, No R
PROG
2.5 µA
PROG Pin Source Current, ∆V
PROG
≤ 5mV ●300 µA
V
PROG
PROG Pin Voltage R
PROG
=19.6k 2.457 V
V
ACPR
ACPR Pin Output Low Voltage I
ACPR
= 5mA 0.7 1.2 V
I
CHRG
CHRG Pin Weak Pull-Down Current V
CHRG
= 1V 15 35 55 µA
V
CHRG
CHRG Pin Output Low Voltage I
CHRG
= 5mA 0.6 1.2 V
V
SEL
SEL Pin Threshold ●0.3 2 V
ORDER PART
NUMBER
(Note 1)
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
LTC1732EMS-4
LTC1732EMS-4.2
T
JMAX
= 140°C, θ
JA
= 180°C/W
ABSOLUTE MAXIMUM RATINGS
W
WW
U
PACKAGE/ORDER INFORMATION
W
UU
MS10 PART MARKING
LTNJ
LTUA
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 6V unless otherwise noted.
ELECTRICAL CHARACTERISTICS
1
2
3
4
5
BAT
SEL
CHRG
TIMER
GND
10
9
8
7
6
ACPR
SENSE
V
CC
DRV
PROG
TOP VIEW
MS10 PACKAGE
10-LEAD PLASTIC MSOP
Consult factory for parts specified with wider operating temperature ranges.
3
LTC1732-4/LTC1732-4.2
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
I
C/10
End of Charge Indication Current Level R
PROG
= 19.6k, R
SENSE
= 0.2Ω●25 50 100 mA
t
TIMER
TIMER Accuracy C
TIMER
= 0.1µF10%
V
RECHRG
Recharge Battery Voltage Threshold per Cell V
BAT
from High to Low (LTC1732-4) 3.72 3.80 V
V
BAT
from High to Low (LTC1732-4.2) 3.95 4.05 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.
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 6V unless otherwise noted.
ELECTRICAL CHARACTERISTICS
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Trickle Charge Current vs VCC Program Voltage vs Temperature Timer Accuracy vs Temperature
Trickle Charge Threshold Voltage
vs Temperature Timer Accuracy vs VCC
Trickle Charge Current vs
Temperature
V
CC
(V)
4
I
TRKL
(mA)
12
1732 G01
6810
60
55
50
45
40
R
PROG
=19.6kΩ
R
SEN
= 0.2Ω
V
BAT
= 2V
T
A
= 25°C
TEMPERATURE (°C)
–50 –25
V
PROG
(V)
1732 G02
05025 75 125
100
2.470
2.465
2.460
2.455
2.450
V
CC
= 6V
R
PROG
= 19.6kΩ
TEMPERATURE (°C)
–50 –25
T
TIMER
(%)
1732 G03
05025 75 125
100
110
105
100
95
90
V
CC
= 6V
C
TIMER
= 0.1µF
TEMPERATURE (°C)
–50 –25
V
TRKL
(V)
1732 G04
05025 75 125
100
2.470
2.465
2.460
2.455
2.250
V
CC
= 6V
V
CC
(V)
412
6810
T
TIMER
(%)
1732 G05
110
105
100
95
90
C
TIMER
= 0.1µF
V
BAT
= 3V
T
A
= 25°C
I
TRKL
(mA)
60
55
50
45
40
TEMPERATURE (°C)
–50 –25
1732 G06
05025 75 125
100
R
PROG
=19.6kΩ
R
SEN
= 0.2Ω
V
BAT
= 2V
V
CC
= 6V
4
LTC1732-4/LTC1732-4.2
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Battery Charge Current vs
Temperature Trickle Charge Threshold Voltage
vs VCC Program Pin Voltage vs VCC
Battery Charge Current vs VCC
Recharge Threshold Voltage vs
Temperature
V
CC
(V)
4
I
BAT
(mA)
12
1732 G10
6810
520
515
510
505
500
495
490
485
480
R
PROG
=19.6kΩ
R
SEN
= 0.2Ω
V
BAT
= 3V
T
A
= 25°C
TEMPERATURE (°C)
–50 –25
V
RECHRG
(V)
1732 G11
05025 75 125
100
4.1
4.0
3.9
3.8
3.7
LTC1732-4.2
LTC1732-4
V
CC
= 6V
I
BAT
(mA)
540
530
520
510
500
490
480
470
460
TEMPERATURE (°C)
–50 –25
1732 G07
05025 75 125
100
R
PROG
=19.6kΩ
R
SEN
= 0.2Ω
V
BAT
= 3V
V
CC
= 6V
V
CC
(V)
4
V
TRKL
(V)
12
1732 G08
6810
2.480
2.475
2.470
2.465
2.460
2.455
2.450
2.445
2.440
R
PROG
=19.6kΩ
T
A
= 25°C
V
CC
(V)
4
V
PROG
(V)
12
1732 G09
6810
2.480
2.475
2.470
2.465
2.460
2.455
2.450
2.445
2.440
R
PROG
=19.6kΩ
T
A
= 25°C
V
BAT
= 3V
5
LTC1732-4/LTC1732-4.2
PIN FUNCTIONS
UUU
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, CTIMER, to GND. The timer period is tTIMER
(hours) = (CTIMER • 3 hours)/(0.1µF). When the TIMER pin
is connected to VCC, 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. If a PNP pass transistor is used, select
a high beta transistor to minimize the charge current error
due to the base current.
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 adapter) greater than the undervoltage
lockout threshold 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.
6
LTC1732-4/LTC1732-4.2
BLOCK DIAGRA
W
–
+
–
+
–
+
–
+
LOGICACPR
C1
–
+
C4
–
+
–
+
C3 A1
CA
C2
VA
CHARGE
GND
1732 BD
PROG
BATTERY CURRENT I
BAT
= (2.457V • 800Ω)/(R
PROG
• R
SENSE
)R
PROG
V
REF
2.457V
LBO
80Ω
V
CC
800Ω54mV
R
SENSE
SENSE
DRV
BAT
720Ω
35µA
TIMER OSCILLATOR
V
REF
COUNTER
STOP RECHRG
SHDN SLP
C/10 C/10
2.5µA
V
CC
CHRG
5
6
3
4
ACPR
10
9
8
7
1
SEL 2
+
–
–
+
C5
3.8V (LTC1732-4)
4.05V (LTC1732-4.2)
UVLO
UNDERVOLTAGE
LOCKOUT
V
UV
= 4.1V
7
LTC1732-4/LTC1732-4.2
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 on the 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.
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.
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 function as 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
(I
CC
= 1mA). 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.
OPERATIO
U
8
LTC1732-4/LTC1732-4.2
R
PROG
= (2.457V/500mA)(800Ω/0.2Ω) = 19.656k
For best stability over temperature and time, 1% resistors
are recommended. The closest 1% resistor value is 19.6k.
Programming the Timer
The programmable timer is used to terminate the charge
cycle. The length of the timer is programmed by an
external capacitor at the TIMER pin. The total charge time
is:
Time = (3 Hours)(C
TIMER
/0.1µF)
The timer starts when an input voltage greater than 4.1V
is applied and the program resistor is connected to ground.
After a time-out occurs, the CHRG output will turn into a
high impedance state to indicate that the charging has
stopped. Connecting the TIMER pin to V
CC
disables the
timer and also puts the charger into a constant-current
mode. To disable only the timer function, short the TIMER
pin to GND.
Battery Detection and Recharge
LTC1732-4: replacing the battery before the timer has ex-
pired will reset the timer, thus starting a new charge cycle,
provided the cell voltage of the new battery is less than
3.8V. If the new battery is greater than 3.8V, the timer will
not be reset and charging will continue for the remaining
portion of the time period. Replacing the battery after the
timer has expired will start a new charge cycle, regardless
of the battery voltage, provided the previous battery volt-
age exceeded 3.9V before the timer expired. After a com-
plete charge cycle has occurred (V
BAT
> 3.9V), and the
battery remains connected to the charger, a new charge
cycle will begin if the battery voltage drops below 3.8V
because of a load on the battery or self discharge.
LTC1732-4.2: replacing the battery before the timer has
expired will reset the timer, thus starting a new charge
cycle, provided the cell voltage of the new battery is less
than 4.05V. If the new battery is greater than 4.05V, the
timer will not be reset and charging will continue for the
remaining portion of the time period. Replacing the battery
after the timer has expired will start a new charge cycle,
regardless of the battery voltage, provided the previous
battery voltage exceeded 4.1V before the timer expired.
APPLICATIONS INFORMATION
WUUU
Charger Conditions
The charger is off when any of the following conditions exist:
the V
CC
pin voltage is less than 4.1V, the dropout voltage
(V
CC
– V
BAT
) is less than 54mV, or if the program resistor
is floating. The DRV pin is pulled up to V
CC
thus keeping the
MOSFET off, and the internal resistor divider is disconnected
to reduce the 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 200mV of 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:
IV
RR
BAT PROG SENSE
=Ω2 457 800. •
where R
PROG
is the total resistance from the PROG pin to
ground.
For example, if 0.5A charge current is needed, select a
value for R
SENSE
that will drop 100mV at the maximum
charge current. R
SENSE
= 0.1V/0.5A = 0.2Ω, then calculate:
9
LTC1732-4/LTC1732-4.2
After a complete charge cycle has occured (V
BAT
> 4.1V),
and the battery remains connected to the charger, a new
charge cycle will begin if the battery voltage drops below
4.05V because of a load on the battery or self discharge.
For either version, to force a new charge cycle, regardless
of previous conditions, momentarily lift the program
resistor or remove and reapply the input power.
CHRG Status Output Pin
When the charge cycle starts, the CHRG pin is pulled down
to ground by an internal N-channel MOSFET that can drive
an LED. When the battery current drops to 10% of the full-
scale current (C/10), the N-channel MOSFET is turned off
and a weak 35µA current source to ground is connected
to the CHRG pin. A 15ms time delay is included to help
prevent false triggering due to transient currents. The
end-of-charge comparator is disabled in trickle charge
mode. After the timer expires, the charge cycle ends, and
the pin goes into a high impedance state. The timer is used
to terminate the charge cycle. By using two different value
pull-up resistors, a microprocessor can detect three states
from this pin (charging, C/10 and stop charging). See
Figure 1.
When the LTC1732 is in charge mode, the CHRG pin is
pulled low by the internal N-channel MOSFET. To detect
this mode, force the digital output pin, OUT, high and
measure the voltage at the CHRG pin. The N-channel
MOSFET will pull the pin low even with a 2k pull-up
resistor. Once the charge current drops to 10% of the full-
scale current (C/10), the N-channel MOSFET is turned off
and a 35µA current source is connected to the CHRG pin.
The IN pin will then be pulled high by the 2k pull-up. By
forcing the OUT pin into a high impedance state, the
current source will pull the pin low through the 400k
resistor. When the internal timer has expired, the CHRG
pin will change to high impedance state and the 400k
resistor will then pull the pin high to indicate the charging
has stopped.
ACPR Output Pin
The LTC1732 has an ACPR output pin to indicate that the
input supply (wall adapter) is higher than 4.1V and 54mV
above the voltage at the BAT pin. When both conditions are
met, the ACPR pin is pulled down to ground by an
N-channel MOSFET that is capable of driving an LED.
Otherwise, this pin is in a high impedance state.
End of Charge (C/10) Output
The LTC1732 includes a comparator to monitor the charge
current to detect an end-of-charge condition. This com-
parator does not terminate the charge cycle, but provides
an output signal to indicate a near full charge condition.
The timer is used to terminate the charge cycle. When the
battery current falls below 10% of full scale, the compara-
tor trips and turns off the N-channel MOSFET at the CHRG
pin and switches in a 35µA current source to ground. A
15ms time delay is included to help prevent false trigger-
ing due to transient currents. The end-of-charge compara-
tor is disabled in trickle charge mode.
Output Voltage Selection
The float voltage at the BAT pin can be selected by the SEL
pin. Shorting the SEL pin to ground will set the float
voltage to 4.1V, while connecting it to V
CC
sets it to 4.2V.
This feature allows the charger to be used with different
types of Li-Ion cells. When charging 4.1V cells, use the
LTC1732-4 with the SEL pin grounded. The LTC1732-4
can also be used for charging 4.2V cells by connecting
the SEL pin to V
CC
. The recharge threshold level is preset
to 3.8V, thus allowing either 4.1V or 4.2V cells to be
charged. Because the recharge threshold voltage level of
the LTC1732-4.2 is preset for 4.05V, this version is
not
recommended for 4.1V cells.
APPLICATIONS INFORMATION
WUUU
Figure 1. Microprocessor Interface
2k
400k
CHRG
1732 F01
V
CC
V
DD
LTC1732
V
+
OUT
µPROCESSOR
IN
3
8
10
LTC1732-4/LTC1732-4.2
Li-Ion Linear Charger Using a PNP Transistor
TYPICAL APPLICATIO S
U
V
CC
V
IN
= 6V
SENSE
DRV
R2
1k R
SENSE
0.2Ω
R3
10k
R
PROG
19.6k
4.1V
Li-Ion
CELL
LTC1732-4
BAT
CHRG 9
8
MBRM120T3
C2
10µF
C1
1nF
1732 TA02
C3
1µF
I
BAT
= 500mA
+
C
TIMER
0.1µF
Q1
2N5087
7
1
6
5
3
4TIMER
PROG
GND
2
SEL
ACPR
10
R1
1k Q2
ZTX749
Gate Drive
Typically the LTC1732 controls an external P-channel
MOSFET to supply current to the battery. An external PNP
transistor can also be used as the pass transistor instead
of the P-channel MOSFET. Due to the low transconductance
of the current amplifier (CA), a high gain Darlington PNP
transistor is required to avoid excessive charge current
error. The transconductance of the current amplifier is
around 0.6µA/mV. For every 1µA of base current, a 1.6mV
of gain error shows up at the inputs of CA. With R
PROG
=
19.6k (100mV across R
SENSE
). This represents a 1.6%
error in charge current.
Constant-Current Only Mode
The LTC1732 can be used as a programmable current
source by connecting the TIMER pin to VCC. This is
particularly useful for charging NiMH or NiCd batteries. In
the constant-current only mode, the timer and voltage
APPLICATIONS INFORMATION
WUUU
amplifier are both disabled. An external termination method
is required to properly terminate the charging by floating
the PROG pin.
Stability
The charger is stable without any compensation when a
P-channel MOSFET is used as the pass transistor and
the battery is present. A 10µF tantalum capacitor is
recommended at the BAT pin to keep the ripple voltage
low when the battery is disconnected. A ceramic output
capacitor may also be used, but because of the very low
ESR and high Q characteristics of multilayer ceramic
capacitors, it may be necessary to add a 1Ω resistor in
series with the ceramic capacitor to improve voltage
mode stability.
If a PNP transistor is used for the pass transistor, a 1000pF
capacitor is required from the DRV pin to V
CC
. To help
stablize the voltage loop a 10µF tantalum capacitor at the
BAT pin is also recommended when a battery is not
present.
11
LTC1732-4/LTC1732-4.2
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.
Dimensions in inches (millimeters) unless otherwise noted.
MS10 Package
10-Lead Plastic MSOP
(LTC DWG # 05-08-1661)
U
PACKAGE DESCRIPTIO
MSOP (MS10) 1100
* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH,
PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
0.021 ± 0.006
(0.53 ± 0.015)
0° – 6° TYP
SEATING
PLANE
0.007
(0.18)
0.043
(1.10)
MAX
0.007 – 0.011
(0.17 – 0.27) 0.005 ± 0.002
(0.13 ± 0.05)
0.034
(0.86)
REF
0.0197
(0.50)
BSC
12345
0.193 ± 0.006
(4.90 ± 0.15)
8910 76
0.118 ± 0.004*
(3.00 ± 0.102)
0.118 ± 0.004**
(3.00 ± 0.102)
12
LTC1732-4/LTC1732-4.2
LINEAR TECHNOLOGY CORPO RATION 2000
sn1732 1732fs LT/TP 0501 2K • PRINTED IN THE USA
PART NUMBER DESCRIPTION COMMENTS
LT®1510-5 500kHz Constant-Voltage/Constant-Current Battery Charger Most Compact, Up to 1.5A, Charges NiCd, NiMH, Li-Ion Cells
LT1512 SEPIC Battery Charger V
IN
Can Be Higher or Lower Than Battery Voltage, 1.5A Switch
LTC1541 Op Amp, Comparator and Reference with 5µA I
CC
Low Cost Linear Charger—See Design Note 188
LT1620 Rail-to-Rail Current Sense Amplifier Precise Output Current Programming, Up to 32V V
OUT
, Up to 10A I
OUT
LTC1729 Termination Controller for Li-Ion Time or Charge Current Termination, Automatic Charger/Battery
Detection, Status Output, Preconditioning, 8-Lead MSOP
LTC1730 Li-Ion Pulse Charger Minimum Heat Dissipation; No Reverse Current Diode Needed; No
MOSFET Required; Limits Charge Current for Safety
LTC1734 ThinSOTTM Li-Ion Linear Battery Charger Only Two External Components; Charge Termination and Gas Gauging
Provided by Monitoring V
PROG
Pin.
RELATED PARTS
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear-tech.com
Single Cell 4.1V, High Efficiency 1.5A Li-Ion Battery Charger
V
CC
V
IN
6V
SENSE
DRV
R3
0.082Ω
1/4W
D2
MBRS130LT3
D1
MBRS130LT3
R4
19.6k 1-CELL
Li-Ion
BATTERY
+
LTC1732-4
BAT
CHRG 9
8
2
7
1
LTC1693-5 4
8
1732 TA03
C2
22µF
C1
0.1µF
Q2
Si2305DS
7
1
6
5
3
R1
1k
1k
4TIMER
PROG
GND
2
SEL
ACPR
10
C4
0.47µF
R2
4.7Ω
+
C3
220µF
15µH
CDRH6D28-150NC
+
U
TYPICAL APPLICATIO
ThinSOT is a trademark of Linear Technology Corporation.
