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BQ76940: Cell ballancing stopping issue of BQ76940

Jimmy Zhou95
Intellectual 870 points
Part Number: BQ76940

Hi All,

One question from my customer is BQ76940 cell ballancing. As we know, to control the balancing of BQ76940, we need to manipulate CELLBAL1, CELLBAL2 and CELLBAL3. But we find that ballancing will not be stopped when we set CELLBAL1, CELLBAL2 and CELLBAL3 to 0 simplely. If we  set CELLBAL1, CELLBAL2 and CELLBAL3 to 0 first and  read CELLBAL1, CELLBAL2 and CELLBAL3 register, cell ballancing will be stopped. 

Can you give out a reasonable explaination of this? 

Jimmy 

Best regards!

  • 0
    TI__Expert 5090 points

    Hi Jimmy,

    Our expert on this device is on vacation right now, but in my limited experience with this device, I am not familiar with this case.  I wonder if you may have some issue involving your serial bus communication, in that the transaction didn't entirely complete until you initiated the next transaction?  

    In case this is related to some delay, how long did you wait after writing the CELLBAL registers before reading them?

    You might try experimenting with other types of transactions, to see if any transaction affects this behavior, or it is closely linked to you reading those specific registers. For example, if you write the CELLBAL registers a second time, does balancing then stop?  Or if you read some other register than a CELLBAL register, does it also stop?

    Thanks,

    Terry

  • 0 in reply to -Terry
    TI__Guru 54715 points

    Hi Jimmy,

    No extra read is needed when balancing is turned off, however it will take some time for the command to stop balancing to take effect.  Balancing changes the 250 ms time line of the part.  When the write of 0 is received in the register it may need to be sent to the upper group which can take some time.  The read you mention likely takes time which allows the balance to stop.  Balance current can stop without aligning to the timeline.

    Starting balancing is similar with the write to start asynchronous to the device timeline.  Commands for the upper cell groups will have an internal communication delay to reach the upper group.

    For a description of timing with balance see the application note http://www.ti.com/lit/pdf/slua775