BQ29312A Datasheet, PDF (26/35 Pages) Texas Instruments – TWO-CELL, THREE-CELL, AND FOUR-CELL LITHIUM-ION OR LITHIUM-POLYMER BATTERY PROTECTION AFE

bq29312A
SLUS629A – JANUARY 2005 – REVISED AUGUST 2005
www.ti.com
APPLICATION INFORMATION (continued)
The disadvantages is that during 0-V charging, bq29312A is inactive. The device does not protect the battery
and does not update battery information (now is 0 V charging) to the PC.
There are two advantage of this configuration:
1. The voltage between BAT and PACK is lower. Higher precharge current is allowed due to less heat loss in
the FET, and no external resistor is required.
2. The charge FET is turned on during precharging. The precharge current can be fully controlled by the
charger.
Charger
DSG-FET
CHG-FET
Pack+
CC
I_(ZVCHG)
DC Input
Battery
DSG
BAT
bq29312A
CHG
PACK
ZVCHG
REG
OD ^PMS
I_(FASTCHG)
CV
4.7 mF
NC
I_(ZVCHG) = 0 V Precharge Current
I_(FASTCHG) = Fast Current
Figure 11. Common FET Mode Circuit Diagram
The signal timing during the common FET mode is shown in Figure 12. The CHG-FET is turned on when the
charger is connected. As V_(BAT) rises and V_(PACK) reaches the bq29312A minimum supply voltage, the REG
output becomes active and the host controller starts to work.
When V_(PACK) becomes high enough, the host controller turns ON the DSG-FET. The charger enters the fast
charging mode when V_(BAT) reaches the fast charge level.
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