Hello all,
We have a 3S2P Li-ion battery pack designed around the BQ20Z655-R1 reference design. 3 out of 10 prototype packs have failed, and all in the same way. After being fully exercised (comm test, charge/discharge test), all 10 were shipped from the manufacturer to the customer. At the customer site, these 3 packs failed shortly after being taken out of their boxes.
Upon opening the packs and taking out the boards, it was determined that all 3 packs showed a short circuit internal to the BQ20Z655-R1 IC. Specifically, after removing the IC from the PCB, pins 32 and 31 (REG25 and VSS) were found to be shorted together. What are the possible failure mechanisms?
The 5 signals that are available from inside the pack to outside are:
PACK+
GND
SMBD
SMBC
ALERT#
Of those lines, PACK+, SMBD, and SMBC have explicit ESD protection.
