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BQ769142: Status of BQ when LDOs are of but FETs are still connected

Gr?nwald Martin
Prodigy 35 points
Part Number: BQ769142

Hello,

we currently have a strange issue where the BQ seems to be still active, because the FETs are still closed, but the BQ has shut down the LDOs.

This leads to a problem in our design where a MCU and CAN Transceiver are powered by the AFE. When the AFE shuts down the LDO it is not possible to see the real status of the battery because the MCU as well as the CAN Transceiver are dead.

Generally this could be acceptable but really dangerous is the fact that in this case the AFE seems to be sitll working and the FETs are still closed so power can be on the outer terminals although the battery looks like in shutdown state for the environmental system.

Do you have an idea what could cause this status/issue to happen? What could be the conditions to get in this situation ?

According to the datasheet it looks like it can not be that the LDOs (and thus the rest of the BMS) are off but the FETs are still driven by the AFE.

Thank you!

Best regards,

Martin

  • 0
    TI__Guru* 81035 points

    Hi Martin,

    This is definitely a strange behavior. The AFE does not have any normal states that would keep the FETs enabled while shutting down the LDOs. Are you using the BREG pin to control an NPN transistor to regulate the REGIN voltage? Can you measure the voltages on REGIN and BREG when the device is in this condition?

    Best regards,

    Matt