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BQ76952: Can we use P-FETs for external balancing in Bq76952 stacked configuration

harish naidu
Prodigy 100 points
Part Number: BQ76952
Other Parts Discussed in Thread: TIDA-01093, BQ76930

HI

Can we use P-FETs for external balancing in Bq76952 stacked configuration or do we need to use N-ch FETs.

Any application note or reference design would help.

Thanks

Harish

  • 0
    TI__Mastermind 42060 points

    Hello Harish,

    Yes, you could use P-FETs for external cell balancing. 

    But depending on how cells attached, it may be better to use N-Ch FETs instead. It is possible during cell attachment for the P-FETs to briefly turn-on, this could continue down the stack and potentially pull-up the VC0 pin, causing damage. If P-FETs are used, it would be advisable that BAT- is connected first to Vss/VC0 prior to the rest of the cells being attached. So only the order of attachment would be the change.

    As for app notes, see the Cell Balancing With BQ769x2 Battery Monitors application note for reference. 

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 100 points

    HI Luis

    Thanks for your feedback

    As per TIDA-01093 schematic for stacked configuration using Bq76903 they have used P-FETs for external cell balancing

    Even we have referred the same

    Thanks

    Harish

  • 0 in reply to harish naidu
    TI__Mastermind 42060 points

    Hello Harish,

    Yes, as I said, it may be okay. But you would just have to be careful on the cell attachment order.

    Even for the BQ76930, there were documents explaining the limitations of using P-FETs. Like those described in Section 4 Cell Balance and Section 10 Random Cell Connection – Within Limits of the bq769x0 Family Top 10 Design Considerations application note. Keep in mind this application note is for the BQ769x0 family of devices, which is a previous generation device family.

    If you already considered the limitations of using P-FETs vs. N-FETs, it is okay to use them.

    Best Regards,

    Luis Hernandez Salomon