Datasheet

V
IN
V
TH
I
PRE
1
2
I
CHG
I
MAX-CHG
I
TAPER
V
BAT
V
BOOST
V
FLOAT
V
RCH
V
BI
bq24450
www.ti.com SLUS929C –APRIL 2009– REVISED FEBRUARY 2012
Figure 7.
Further Improvements to the Circuit of Figure 6
In applications where the load current is low, the current through the V
BAT
voltage divider can be a non-negligible
proportion of the load current. Current flowing back thorough Q
EXT
when the input power is removed constitutes
another drainage path. The modifications in Figure 8 fix both these issues.
The addition of D
EXT
(see Figure 8) fixes the reverse current problem. Returning the voltage feedback divider
chain to the PGOOD pin instead of to GND ensures that the divider does not draw any current when the input
supply is not present. (When sinking 50μA, the saturation voltage of the PGOOD transistor is typically only
30mV).
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