LTC1732-4 LINER [Linear Technology], LTC1732-4 Datasheet - Page 7

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

OPERATIO
The LTC1732 is a linear battery charger controller. The
charge current is programmed by the combination of a
program resistor (R
and a sense resistor (R
pins. R
trimmed 800 resistor setting up a voltage drop from V
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
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
Charging begins when the potential on the V
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
When the battery approaches the final float voltage, the
charge current will begin to decrease. When the current
PROG
sets a program current through an internal
SENSE
SENSE
U
, thus reducing the charge current.
PROG
SENSE
and R
) from the PROG pin to ground
) between the V
PROG
.
SENSE
CC
CC
and SENSE
which sets
pin rises
CC
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
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
high and clamp it at 3.5V.
When the input voltage is not present, the charger goes
into a sleep mode, dropping I
reduces the current drain on the battery and increases the
standby time.
CC
CC
= 1mA). An internal current source will pull this pin
. When in the constant-current only mode, the
LTC1732-4/LTC1732-4.2
CC
to 7 A. This greatly
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