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BQ40Z80: IC Catastrophic failure

Theodore Beauchant
Prodigy 105 points
Part Number: BQ40Z80

Hi,

We're having an issue with the BQ40Z80 in a 6 cell configuration where the IC suddenly suffers a catastrophic failure. There is a small hole in the IC  package, likely causing an internal short as the package remains very hot afterwards.

From the looks of it, it seems the failure happens when the battery is plugged in to its load, however we don't have a 100% certainty on this as it could also have happened during storage.

The issue is not systematic, we have both had packs with no issue (so far) and packs with issues.

We also noticed that the TVS diodes on the SMB line on the load side failed short after the event.

The exact same board with the exact same load has worked perfectly for years in a 5S configuration. I am of course ready to transmit schematics and srec file for the pack.

Help will be much appreciated.

Thanks,

Theo

  • 0
    TI__Guru** 105590 points

    Hello Theo,

    Could you share the layout and schematic files?

    I have not seen this kind of failure before, so it is most likely something on the system level that is getting to the gauge. It seems it may be coming on the SMB lines as a high power ESD event since the TVS has also failed.

    To get a better idea of what may have happened we would need more information on the cause of the failure, which may be hard to gather information on.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 105 points

    Hi Wyatt,

    Thanks for your very fast reply. I will send the schematics via DM quickly.

    I have the same feeling, ie. something around the rest of the system that would be sending a large surge in voltage up to the BMS.

    The I2C lines on the system side are pulled up via 2.2K resistors to the +3.3V power rail and then go directly to the I2C pins of an STM32MP157C. According to the BQ40Z80 datasheet the lines are able to withstand +35V. I doubt 35V could have appeared on the STM32 without much more damage to the board than a couple ESD diodes.

    I will try to check if there is anything on the main power line that could send that kind of surge. We do have some small inductive loads down the chain (motors), but they are through a local +5V supply and again, I would expect more damage locally if there was a 35V surge on these +5V rails.

    If you could give a look at the schematics and make sure there isn't anything stupid in there that would be great. Also if there's any configuration settings that might cause something like this?

    Thanks for the help,

    Theo

  • 0 in reply to Theodore Beauchant
    TI__Guru** 105590 points

    Hello Theo,

    I was not able to open the schematic files, see the PM.

    There's nothing in the configuration of the gauge that could cause it to blow up like this, it must be from an outside source. If the source of the ESD event happened closer to the gauge and the gauge too the majority of the damage I would suspect the other devices on the bus may not be as damaged as the gauge.

    Sincerely,

    Wyatt Keller