BQ2947_16 Datasheet, PDF (8/24 Pages) Texas Instruments – Overvoltage Protection for 2-Series to 4-Series Cell Li-Ion Batteries

bq2947
SLUSB15E – SEPTEMBER 2012 – REVISED FEBRUARY 2016
8 Detailed Description
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8.1 Overview
The bq2947 is a second level overvoltage (OV) protector. Each cell is monitored independently by comparing the
actual cell voltage to a protection voltage threshold, V_OV. The protection threshold is preprogrammed at the
factory with a range between 3.85 V and 4.65 V.
8.2 Functional Block Diagram
Figure 7 shows a CMOS Active High configuration.
PACK+
R_VD
VDD
1
C_VD
R_IN
V4
2
C_IN
R_IN
V3
3
C_IN
R_IN
V2
4
C_IN
R_IN
V1
5
C_IN
VSS
6
V_OV
Enable
Delay Charge/ ^Active
Discharge Circuit
OUT
8
9
PWPD
7
CD
C_CD
PACK–
Figure 7. Block Diagram
NOTE
In the case of an Open Drain Active Low configuration, an external pull-up resistor is
required on the OUT terminal.
8.3 Feature Description
In the bq2947 family of devices, if any cell voltage exceeds the programmed OV value, a timer circuit is
activated. This timer circuit charges the CD pin to a nominal value, then slowly discharges it with a fixed current
back down to VSS. When the CD pin falls below a nominal threshold near VSS, the OUT terminal goes from
inactive to active state. Additionally, a timeout detection circuit checks to ensure that the CD pin successfully
begins charging to above VSS and subsequently drops back down to VSS, and if a timeout error is detected in
either direction, it will similarly trigger the OUT pin to become active. See Figure 9 for details on CD and OUT pin
behavior during an overvoltage event.
8
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