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BQ77905: how to detect that BQ77905 is charging or discharging.

Yue TANG
Expert 8695 points
Part Number: BQ77905
Other Parts Discussed in Thread: BQ76920

Hi experts,

My customer checked with me  how to use a MCU to detect that BQ77905 is charging or discharging? can you recommend a solution for this? 

  • 0
    TI__Guru* 81034 points

    Hi Yue,

    The BQ77905 does have an internal state comparator to determine whether the battery is charging or discharging. However, the state comparator is not observable from the outside and is only turned on during faults where only one of the FETs is disabled.

    If the customer needs more information, I recommend using a battery monitor like the BQ76920. It has all of the protection features, but it also can report current, cell voltages, and temperatures to the MCU.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    TI__Expert 8695 points

    Matt,

    i'm afraid that the design is fixed, can you please suggest a solution based on BQ77905? Is there a feasible way  to use a mcu  or an  external circuit to get this state ? thanks.

  • 0 in reply to Yue TANG
    TI__Guru* 81034 points

    Hi Yue,

    The BQ77905 cannot report whether charge or discharge is occurring. There is no example solution for this case.

    I have heard of cases where users have placed a comparator on the SRN pin to try to detect charging or discharging. If the MCU has an ADC, maybe they can add a circuit to measure the SRN voltage with the ADC of the MCU. 

    Best regards,

    Matt