BQ29312_15 Datasheet, PDF (27/39 Pages) Texas Instruments – FOUR CELL LITHIUM-ION

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bq29312
SLUS546E – MARCH 2003 – REVISED MARCH 2005
APPLICATION INFORMATION (continued)
The disadvantages is that during 0 V charging, bq29312 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 is
the FET and no external resistor 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
bq29312
CHG
PACK
ZVCHG
REG
OD ^PMS
I_(FASTCHG)
CV
4.7 µF
NC
I_(ZVCHG) = 0 V Percharge 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 bq29312 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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