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Original question:

BQ27426: Some questions about FCC and RM updates in battery application scenarios

BQ27426: FCC changes, RM doesn't change scenarios

Wang Dong
Intellectual 600 points
Part Number: BQ27426


Tool/software:

Hi there

VatChgTerm is set incorrectly in our app(Should be 4400mV, but incorrectly set to 4252mV), causing the FCC to drop on first charge. We measured it and the FCC dropped, but the RM did not.

May I ask if there are any other parameters other than VatChgTerm parameter setting error that can cause similar phenomenon when FCC changes but RM doesn't? If so, please help to list them.

我们应用程序中的 VatChgTerm 设置不正确（应该是4400mV，错误的设置为了4252mV），导致首次充电时 FCC 下降。我们进行了测量，FCC 下降了，但 RM 没有下降。

请问，除了 VatChgTerm 参数设置错误外，是否还有其他参数会导致 FCC 变化而 RM 不变的类似现象？如果有，请帮忙列出。

VatChgTerm_FCC_RM变化.zip

  • 0
    Intellectual 600 points

    Please help reply to the above question, thank you very much!

  • 0 in reply to Wang Dong
    TI__Guru 64816 points

    VatChgTerm is not a static parameter. If you configure the gauge correctly (see TRM, https://www.ti.com/lit/ug/sluubb0/sluubb0.pdf, 7.4.2.3.10) then the gauge will measure this voltage so that FCC is calculated with the correct charging voltage level.

    To answer you second question: The gauge calculates FCC together with RM. FCC (loosely) = initial capacity + RM. Initial capacity is the charge from DOD at End Of Charge (which is a function of VatChgTerm among others) to present DOD (which is a function of DOD0, which is based on previous measurements and coulomb count) and Qmax.

    So if RM stays constant while FCC changes, DOD at EOC (and therefore VatChgTerm) is the most likely parameter that will *only* affect FCC becuase all other parameters affect both FCC and RM.