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BQ40Z50: How to understand Offset Error parameter?

joy zhou1
Intellectual 530 points
Part Number: BQ40Z50

Hi,

Per bq40z50 Technical Reference document, one of QMax Update disqualified conditions is Offset Error.

I don't understand it well, could you please help me to understand it better: 1) "If Offset error accumulated during passed previous OCV reading exceeds 1% of Design Capacity, update is disqualified." Is this meaning, if the passed accumulated capacity is over 1% of design capacity, for example, passed capacity is 3380mah for a brand new battery pack, but design capacity configuration is 3200mah, then QMax Update is disqualified and QMax will not update?  2) "Offset error current is calculated as CC Deadband/Sense resistor value." Is this meaning how to configure Offset Error? Means Offset Error=CC Deadband/sense resistor value?

Please clarify.

Thanks,

Joy

  • 0
    TI__Guru 61516 points

    QMax is calculated by integrating the current over the sense resistor (passed charge) between two qualified OCV measurements and dividing this by the change in depth of discharge of the cell. For this to be accurate, there are several rules (for example, minimum passed charge, OCV measurements must not be in the flat zone of the voltage curve etc.).

    The coulomb counter has a offset error that will accumulate over time so if the discharge is very slow and/or there aren't qualifying OCV measurements, the accumulated error in passed charge due to this offset error would interfere with QMax accuracy so the gauge will reject it if this error exceeds a threshold (which is typically a private parameter).

    For the vast majority of applications, there is no need to change this from the default values.