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BQ27421-G1: Some devices have address 0x21 with values of 0x02 or 0x03.

Shunsuke Yamamoto
Expert 7711 points
Part Number: BQ27421-G1

Hi experts,

 

My customer is going to design with BQ27421-G1.

He referred to "4.15 StateOfHealth(): 0x20 and 0x21" of the bq27421-G1 Technical Reference Manual(Rev. C). In his case, after about five cycles of charge and discharge, some devices have address 0x21 with values of 0x02 or 0x03.

Could you tell me what caused this to happen?

Also, what condition does the value switch under?

He evaluates BQ27421-G1 using the same conditions of batteries and the same conditions of circuits.

 

Best regards,

Shunsuke Yamamoto

  • 0
    TI__Mastermind 27321 points

    Hello Yamamoto,

    The reason the customer might be seeing some devices with 0x02 or 0x03 depends on whether the device learned a new Qmax or is using the default Qmax value.

    SOH = FCC / Design Capacity

    FCC is calculated based on Qmax, so reading from address 0x21 tells the user whether the reported SOH is based on learned Qmax or default Qmax.



    Regards,
    Jose Couso

  • 0 in reply to Jose Couso
    TI__Expert 7711 points

    Hello Jose-san,

    Thank you for your reply.

    I clearly understood the device utilizes learned Qmax or defult Qmax. I also understood that address 0x21 tells the user whether the reported SOH is based on learned Qmax or default Qmax.

    When would the device use default Qmax?

    When would the device use learned Qmax?

    For example, the device sometimes use default Qmax. On the other hand, it sometimes use learned Qmax.

    Best regards,

    Shunsuke Yamamoto

  • 0 in reply to Shunsuke Yamamoto
    TI__Mastermind 27321 points

    Hello Yamamoto,

    The device would use default Qmax when a Qmax hasn't been learned from the gauge or when it uses the programmed Qmax (the one the user inputs in the configuration file).

    In other words, when QMAX_UP bit is set (means the gauge has learned a new Qmax), address 0x21 will return 0x03. 

    Regards,
    Jose Couso