OUT

V4

V3

V1

V2

VSS

VDD

CD

PACK+

PACK–

8

7

9

1

2

3

4

5

6

PWPD

Enable

Active

Delay Charge/

Discharge Circuit

9

bq2947

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SLUSB15F – SEPTEMBER 2012 – REVISED JANUARY 2017

Product Folder Links: bq2947

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8 Detailed Description

8.1 Overview

The bq2947 is a second level overvoltage (OV) protector. Each cell is monitored independently by comparing 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.

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.