LTC1732-4 LINER [Linear Technology], LTC1732-4 Datasheet - Page 9

• Manufacturer Part Number: LTC1732-4
• Description: Lithium-Ion Linear Battery Charger Controller
• Manufacturer: LINER [Linear Technology]

APPLICATIONS
After a complete charge cycle has occured (V
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 35 A 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 35 A current source is connected to the CHRG pin.
The IN pin will then be pulled high by the 2k pull-up. By
Figure 1. Microprocessor Interface
LTC1732
V
V
CC
CHRG
+
8
U
3
INFORMATION
400k
U
2k
OUT
IN
PROCESSOR
W
V
DD
1732 F01
BAT
U
> 4.1V),
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 35 A 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
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 LT1732-4
can also be used for charging 4.2V cells by connecting
the SEL pin to V
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.
LTC1732-4/LTC1732-4.2
CC
. The recharge threshold level is preset
CC
sets it to 4.2V.
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