BQ29312A Datasheet, PDF (24/35 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
APPLICATION INFORMATION (continued)
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20
18
16
V_(PACK)
14
12
V_(BAT)
V_(ZVCHG)=
V_(PACK) - 8 V
10
8
6
4
V_(ZVCHG)= V_(PACK) / 2
2
3.5 V
0
0
4
8
12
t - Time - mS
16
20
Figure 9. Voltage Transition at ZVCHG, PACK, and BAT
As V_(PACK) exceeds 7 V, V_(ZVCHG) = V_(PACK)/2. However, V_(ZVCHG) is maintained to limit the voltage between PACK
and ZVCHG at a maximum of 8 V(typ). This limitation is intended to avoid excessive voltage between the gate
and the source of ZVCHG-FET.
The signal timing is shown in Figure 10. When precharge begins, (V_(BAT) = 0 V) V_(PACK) is clamped to 3.5 V and
holds the supply voltage for bq29312A operation. After V_(BAT) reaches sufficient voltage high enough for
bq29312A operation, the CHG-FET and the DSG-FET are turned ON and ZVCHG-FET is turned OFF.
Although the current path is changed, the same precharging current is still applied. When V_(BAT) reaches the fast
charging voltage (typical 3 V per cell), the charger switches into fast charging mode.
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