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BQ76920: timing of cell balance function relative to configuration register write to enable and disable

ST71353
Prodigy 20 points
Part Number: BQ76920


Hi, we are using cell balancing function in a way where timing of enabling and disabling function is important.

Although the datasheet doesn't seem to explicitly mention, the timing observed is as follows:

* Enable cell balancing: a BQ 250ms interval completes (ALERT is asserted by BQ), immediately issue request to enable cell balance through I2C reg write (~ms latency). On O-scope, enabling is observed to occur the next 250ms interval.

* Disabling cell balancing: a BQ 250ms interval completes, immediately issue request to disable cell balance through I2C write. Disabling observed to occur the current 250ms interval.

Is this known behavior, to have non-uniform enabling / disabling behavior? If this is known, any guidance on how we can make sure this is always the case? Basically if enabling/disabling is off unexpectedly by a 250ms service interval, it may impact behavior of the system. Of course it is also possible we are misinterpreting the behavior, so guidance on expected behavior is helpful.

Thanks

  • 0
    TI__Guru 54715 points

    Hi ST,

    The application note Embedded Scheduler in Cell Battery Monitor of the bq769x0 http://www.ti.com/lit/pdf/slua775 may be helpful.  The part runs on the 250ms timeline and will always be one interval or the next.  The measurement timeline must be changed for balancing.  When the balancing command is issued, the new timeline will start at the next 250 ms boundary.   Once you are balancing and in that 250 ms interval, the timing is committed.  If you turn off the balancing, the current flow can stop, but the timing must finish the 250 ms interval.