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bq76920 external balancing - adjacent cells

FJ
Intellectual 360 points
Other Parts Discussed in Thread: BQ76920

When I turn on cell balancing for a specific cell [CB1]  What is the state of VC1 pin?  

Why can't I balance two adjacent cells if I am external balancing?

Does CB1 have to be set back to off in order to read cell voltage and determine if further cell balance is  required?

  • 0
    TI__Intellectual 2065 points

    When cell balancing is enabled the internal FET will pull the pins associated with that cell together drawing current through the input
    resistors for that cell. For the bq76920 the input resistors can be sized to select the balance current within
    the capability of the part.

    Cell volatges are still converted during cell balancing, but at 12.5 ms decimation period. Refer to sec 7.3.1.1.2 of Datasheet for more details.

    Adjacent cells should not be balanced simultaneously. This may cause cell pins to exceed their absolute maximum conditions and is also not recommended for external balancing implementations. Please refer to Sec 7.3.1.3.3 of Datasheet.

    Thanks,

  • 0 in reply to MS1291
    Intellectual 360 points
    Guess I am not understanding. If two adjacent cells hit max safe voltage while charging am I just supposed to pick which one I want to destroy and which one I want to save?
  • 0 in reply to FJ
    TI__Intellectual 2065 points

    Depending on the charging algorithms used in conjunction with cell balancing,  charging rate will be reduced or cells will have to be continuously  balanced

    Suitable algorithms have to be used in the charge controller.

    Hope this helps.