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BQ40Z50-R2: How does MaxError affect % charge and Remaining Capacity?

Yang Zhang
Prodigy 40 points
Part Number: BQ40Z50-R2

Hi,

Do I understand correctly when Qmax and resistance table not updated after multiple cycles of charging and discharge, max error increase, thus the % charge and the remaining capacity reading is not less accurate? If so, how does MaxError transfer to them? Our device set a minimum 5% charge threshold to shut down. If the MaxError is 50%, and battery has 10% of charge left, does it mean only 5% charge left? 

Does MaxError affect remaining capacity?

Thanks

Yang

  • 0
    TI__Genius 11535 points

    Hi Yang,

    MaxError() is reduced after Qmax and Ra updates. MaxError() increases when those values have not been updated after roughly 20 cycles. MaxError does not impact remaining capacity, Qmax, or Ra.

  • 0 in reply to Jessica H.
    Prodigy 40 points

    Hi Jessica,

    Let me make sure I understand what you said. Regardless the reading of the MaxError, relative % charge and remaining capacity always indicate the actual charge left in the battery. Right?

    If so what is the purpose of the MaxError? In what scenario should it be used?

    Thanks,

    Yang

  • 0 in reply to Yang Zhang
    TI__Genius 11535 points

    Hi Yang,

    MaxError is the expected margin of error, in %, in the state-of-charge calculation. The max error is just an indication of how much accuracy to expect. If you have chosen your ChemID correctly and completed learning cycle, the max error will be 1%. So it means you expect your gauge to be close to being 99% accurate. 

    Relative % charge and remaining capacity are not necessarily the actual charge left in the battery because there could be some error depending on if the gauge is setup properly.

  • 0 in reply to Jessica H.
    Prodigy 40 points

    Hi Jessica,

    Thanks for explain that "MaxError is the expected margin of error in %". Am I right to say if MaxError is 50% and remaining capacity is 1000mAh,  then the actual value could be any where between 500mAh to 1500mAh?

    Thanks,

    Yang

  • 0 in reply to Yang Zhang
    TI__Genius 11535 points

    Hi Yang,

    That is correct; however the error would likely be a lot lower because that is the  maximum error possible.