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BQ40Z50 RunTimeToEmpty() calculation details

Pial
Expert 7280 points

Dear team,

Could you please give us some more details regarding what is returned by RunTimeToEmpty() call ?

From http://www.ti.com/lit/ug/sluua43a/sluua43a.pdf , I don't know if the value is taking into account the LoadMode parameter (=1 for constant power) or if the result is always the result of remaining capacity (mAh) divided by current rate of discharge (mA) ?

If this is the case, then the best way to get an estimation of run time would be to get the remaining capacity (cWh) and current rate of discharge (mW) and divide it in the MCU, right ?

Please feel free to give me a call or take this conversation offline if you need some more details!

All the best,

PA

  • 0
    TI__Expert 7280 points
    PS: Also, is there any link between BatteryMode() CAPM and the IT Configuration Load Mode 0 (constant current) or 1 (constant power) ?
  • 0 in reply to Pial
    TI__Mastermind 34775 points

    Hello Pierre-Alexandre,

    The IT gauge must be used in the load mode that best matches the application. The load mode impacts the gauge algorithm that runs and the accuracy. I would recommend using load mode = 1 (constant power), if that best matches the application. This will most likely impact the RunTimeToEmpty() parameter calculation, but not necessarily the RemainingCapacity(). CAPM setting will affect the display of RemainingCapacity(), but should impact the RunTimeToEmpty().

    So in your case it would be RunTimeToEmpty() in min = RemainingCapacity() in cWh  * 60/ Power() in cW.

  • 0 in reply to Damian Lewis
    TI__Expert 7280 points
    Thanks a lot Damian,

    If I read you correctly, LoadMode should impact RunTImeToEmpty, and CAPM should not ?

    I'll get back to you after some tests are done.

    Best regards,
    PA
  • 0 in reply to Pial
    TI__Mastermind 34775 points

    Hi PA,

    Also check your load select settings as well. For constant power, load select settings 0-6 are good. Pick the option that best suite the application. 

  • 0 in reply to Damian Lewis
    TI__Expert 7280 points

    Hello Damian,

    Thank you! Yes, I already checked this parameter, it was ok.

    FYI, some more tests showed that changing CAPM to 1 modified the result of RunTimeToEmpty().

    RunTimeToEmpty()[min] = 60/10 * RemainingCap() [cWh] / Power()[mWh].

    Still, the result is somehow optimistic, but it's close enough.

    Thanks again,

    All the best,

    PA

  • 0 in reply to Pial
    TI__Mastermind 34775 points

    Hello Pierre-Alexandre,

    Thanks for the feedback. It's better to report  RemainingCap() in the selected load mode.