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bq20z95 discharget FET state during charging

NBA
Prodigy 110 points

Hello,

I've just started looking into the bq20z95 gas gauge, and I have a question about the discharge FET control.

Under what conditions does the discharge FET turn off?  Is it possible to be charging the pack through the charge FET and the discharge FET's body diode?  Or, will the discharge FET always be on when charging is allowed via the charge FET?

Thanks.

  • 0
    TI__Guru 73830 points

    Nathan

    The device normally keeps the CHG and DSG FETs on to provide the lowest resistance path for current. The FETs will turn off in response to fault conditions and they can be configured to turn off at charge complete or discharge complete. Charging is allowed through the body diode of the DSG FET, particularly when it is in the precharge region. But, the device should turn the DSG FET on when charging commences.

    Regards
    Tom

  • 0 in reply to ThomasCosby
    Prodigy 110 points

    Thanks for the quick reply.

    Is the PMS pin the only thing that specifies pre-charging?  And, if PMS is tied to Vss, does that mean that the DSG FET should be on all the time when charging, and not in a fault condition?

  • 0 in reply to NBA
    TI__Guru 73830 points

    Nathan

    The FET control used for pre-charge is set by the ZVCHG0 and ZVCHG1 bits in the Operation Cfg A register. The DSG FET should stay on, unless there is a fault condition forcing it off. The PMS input is another feature that is used when charging when the battery voltage stack is at an extremely low voltage.

    Regards
    Tom