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BQ20Z655-R1 REG25 Failure

Kevin Hughes
Intellectual 300 points
Other Parts Discussed in Thread: BQ20Z655-R1

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.

  • 0
    Intellectual 300 points

    As a followup to this question, we have had a 4th pack fail.  This failure occurred after a communication test, in which the ALERT# pin was incorrectly connected to a GPIO set to Open drain pullup to 3.3V on an STM32F4.  No other pullup was connected.  I do not know how exactly how strong a pullup this would equate to, but it appears to be in the 10s of uA.  Would that be enough to damage the BQ chip?

  • 0 in reply to Kevin Hughes
    TI__Expert 6575 points
    Hi Kevin,
    Some of the pins are pulled up internally, like the PRES, and ALERT and pulling them up externally especially to 3.3V will cause them to back drive and damage the REG25.
    Let me send you a friend request and take this question offline, so that I can look at your schematics.
    Regards,
    Swami