BQ29312_15 Datasheet, PDF (25/39 Pages) Texas Instruments – FOUR CELL LITHIUM-ION

www.ti.com
APPLICATION INFORMATION (continued)
bq29312
SLUS546E – MARCH 2003 – REVISED MARCH 2005
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 bq29312 operation. After V_(BAT) reaches sufficient voltage high enough for bq29312
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.
25