Datasheet
I
IN
I
IN
I
CC
OUT
VDD
CB_EN
GND
1
2
4
3
CD
VC2
VC1
VC1_CB
8
7
5
6
V
CELL
V
CELL
±V
CB
I
CB
I
CB
OUT
VDD
CB_EN
GND
1
2
4
3
CD
VC2
VC1
VC1_CB
8
7
5
6
I
CB_EN
d
CD
DELAY
t
C
X
=
CD
DELAY
d
t C X´=
bq29200
bq29209
SLUSA52A –SEPTEMBER 2010–REVISED NOVEMBER 2010
www.ti.com
TEST CONDITIONS
Figure 4. I
CC
, I
IN
Measurement
Figure 5. I
CB
Measurement
PROTECTION (OUT) TIMING
Sizing the external capacitor is based on the desired delay time as follows:
Where t
d
is the desired delay time and X
DELAY
is the overvoltage delay time scale factor, expressed in seconds
per microFarad. X
DELAY
is nominally 9.0 s/µF. For example, if a nominal delay of 3 seconds is desired, use a C
CD
capacitor that is 3 s / 9.0 s/µF = 0.33 µF.
The delay time is calculated as follows:
If the cell overvoltage condition is removed before the external capacitor reaches the reference voltage, the
internal current source is disabled and an internal discharge block is employed to discharge the external
capacitor down to 0 V. In this instance, the OUT pin remains in a low state.
Cell Voltage > V
PROTECT
When one or both of the cell voltages rises above V
PROTECT
, the internal comparator is tripped, and the delay
begins to count to t
d
. If the input remains above V
PROTECT
for the duration of t
d
, the bq2920x output changes from
a low to a high state, by means of an internal pull-up network, to a regulated voltage of no more than 9.5 V when
I
OH
= 0 mA.
The external delay capacitor should charge up to no more than the internal LDO voltage (approximately 5 V
typically), and will fully discharge in approximately under 100 ms when the overvoltage condition is removed.
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