Datasheet

I-QC
I-QC:Quick-ChargeCurrent
CV
Charger
CHG
PACK
GPOD
PMS
REG
DSG
bq77PL900
Battery
BAT
DSG-FET CHG-FET
PCHG-FET
R
(PCHG)
S0354-01
PACK+
CC
VDS
ID
ID = (VPACK)
M0123-01
bq77PL900
www.ti.com ...................................................................................................................................................... SLUS844B – JUNE 2008 – REVISED JANUARY 2009
Figure 29. 0-V/Precharge FET Circuit in Host-Control Mode
The 0-V/precharge FET is driven by the GPOD output. By setting the GPOD bit to 1, the GPOD output turns ON,
and then the PCHG FET. The 0-V/precharge current is limited by the 0-V/precharge FET (PCHG FET) and a
series resistor (R(PCHG)) as follows.
I
0V/PCHG
= I
D
= ( V
PACK+
– V
BAT
– V
DS
) / R
P
A load curve of the PCHG FET is shown in Figure 30 . When the gate-source voltage (V
DS
) is high enough, the
FET operates in the linear region and has low resistance. By approximating V
DS
as 0 V, the 0-V/precharge
current (I
0V/PCHG
) is expressed as follows.
I
0V/PCHG
= (V
PACK+
– V
BAT
) / R
P
Figure 30. 0V/PCHG FET ID and VDS Characteristics
Copyright © 2008 – 2009, Texas Instruments Incorporated Submit Documentation Feedback 53
Product Folder Link(s): bq77PL900