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BQ76930: 【Bq76930 Cell Balancing】Wrong duty cycle

Kevin Li
Intellectual 300 points
Part Number: BQ76930

Hi ~  here is the problem.

When MCU want to set Balancing channel per 250ms

Some balancing time will disappear.??!!                       Only separate battery will happen.    (Is the cell too lonely so that be lazy?)

Balancing period is 243ms

Command period is 250ms

But It works when I both set CB1 & CB2.   Other Adjacent cells can work too.

because that adjacent cells should not be balanced simultaneously.

I want to balance like below situation

Thanks for your help~~

  • 0
    TI__Guru 54715 points

    Hi Kevin,

    Balancing is duty cycled by the IC for measurement and balancing on the 250 ms internal scheduler time cycle of the device.  When balancing the duty cycle is 70% (balance) on.   See figure 5 in the apnote Embedded Scheduler in Cell Battery Monitor of the bq769x0 for an example.  Also note in figure 5 that the command to balance must be synchronized with the internal timeline, so there is a delay between the write to start balancing and when current begins.  When commanded off, the current can be shut off before the timeline re-adjusts to the non-balancing timing.  That seems to be what is shown in your scope captures.

    Your diagram of balancing every other cell alternately seems correct, but rather than changing at the enabled cells at same rate as the device is cycling (250ms),  you may see a more predictable result if each selection is run some multiple of the internal time, perhaps seconds.