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BQ76940: SYS_STAT reserved bits

Glen Cook
Prodigy 220 points
Part Number: BQ76940

Hi,

We are trying to track down an issue with our battery pack. The issue appears to coincide with bit 6 of the SYS_STAT register being set. In the datasheet, this bit is marked as reserved with no additional information being available.

The bit is obviously being set for some reason, would it be possible to get some more information on what this bit is used for?

Cheers

Glen.

  • 0
    TI__Guru* 81034 points

    Hi Glen,

    This bit is read only and it is the output of a wake detection circuit. Can you explain the problem you are seeing in your battery pack?

    Thanks,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 30 points

    Hi Matt,

    I'm a collegue of Glen's working on the same problem.

    What is the wake detection circuit? What exactly is it detecting? What does that bit mean when it is high? I have not been able to find any references to it in any of the BQ76940 datasheets.

    Many Thanks,

    Ed

  • 0 in reply to g g2
    TI__Guru* 81034 points

    Hi Ed,

    This is a reserved bit and the circuit should not be enabled by default. Can you tell me your settings for the SYS_CRTL2 register? Are you setting the reserved bits in this register to the default values of zero (I believe if these are set to the default values, you should never see the WAKE bit is SYS_STAT)?

    Also, can you please describe the problem you are trying to debug?

    Thanks,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 30 points

    Hi Matt,

    We are having an issue where the quiescent load of some our battery pack is higher than others, leading to unbalanced batteries when the packs have been stored for a while. We suspect this is because the AFE is consuming more current in the packs with the issue.

    We have found that on a pack where this has been occuring, using debugging firmware on our pack microcontroller, this bit is set high when the pack is woken up. We do not set it at any point, and apart from in our debugging firmware, the only time where we do anything with this register is to clear it when our battery pack is woken up from it's sleep mode. When the pack is in sleep mode the AFE's ADCs are turned off.

    What does this pin being high mean? How does what is happening to make this flag go high?

    Regards,

    Ed

  • 0 in reply to g g2
    TI__Guru* 81034 points

    Hi Ed,

    What are your settings for the SYS_CTRL2 register? I believe if the reserved bits are set to their default values, then this WAKE flag cannot go high.

    Thanks,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 30 points

    Hi Matt,

    SYS_CTRL2 is 0b00000011

  • 0 in reply to g g2
    TI__Guru* 81034 points

    Hi Ed,

    If the SYS_CTRL2 and SYS_CTRL1 reserved bits are set to their default values, then it should not be possible for the WAKE bit to set in the SYS_STAT register. Is it possible there are spurious writes from the MCU that could accidentally set these bits?

    How are you entering sleep mode? Do you mean SHIP mode?

    Regards,

    Matt