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BQ29209-Q1: Internal balance failure

Part Number: BQ29209-Q1


The customer design with BQ29209-Q1. BQ29209-Q1 is used to design the balancing circuit of two series cells. After the battery pack is welded and the electrical performance test is completed, it is placed in inventory for 2 months. On return inspection, it is found that the high side battery cell is consumed to 0V (B2)

The protection board was disassembled and confirm leakage current at the BM side abnormally increased to about 0.9mA. Will the power-on sequence of the protection board from B+ ->B- ->BM or BM->B+ ->B- cause the balancing IC to fail?

Will disordered power-on sequence cause IC failure? Is this possible?

The schematic and test as below:

How to resolve this issue?

Waiting for your reply.