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bq33100 resolution of capacitance measurement

Chris Zagel
Prodigy 110 points
Other Parts Discussed in Thread: BQ33100

In accordance with the datasheet of the bq33100 the resolution of the calculated capacitance is in Farad. Are there any possibilities to increase this resolution of the capacitance mesurement of the bq33100?

For example, if I use a stack of 5 capacitors with each 25F @ 2,1V, I get a total capacitance of 25F/5=5F. In this example the resolution of 1F (20% of initial value) is insufficient.

 

 

  • 0
    TI__Expert 6470 points

    Chris,

    I'll have to check the latest datasheet to verify. The resolution is normally 0.1F. In your example, it would report 5.0F, 5.1F, etc.  However, for capacitance of 100F or more, it may be truncated to just one Farad.

    Regards,

    Doug

     

  • 0 in reply to Doug Williams4811
    Prodigy 110 points

    Dear Doug,

    Thanks for your fast response.

    Please can you check if the resolution is 100mF, I'm skeptical because register DF:System Data:Data:Capacitance is an integer value and has the unit Farad.

    Otherwise the resolution should increase, if I emulate a much higher discharge current through a wrong internal shunt-resistor value?

    How can I normally tell the bq33100 what the value of the shunt, or will this value be calculated? 

    Regards,

    Chris

  • 0 in reply to Chris Zagel
    TI__Expert 6470 points

    Hi Chris,

    For normal values, it is definitely 100mF. For very low values, the resolution may improve, but I don't have a way to test it right now. I think the only open question is whether the resolution still maintains 100mF at calculated capacitance values above 99.9F. Sorry we have such a fundamental error in the datasheet.

    The sense resistor value can be found by running the current calibration utility on the calibration screen, or by just typing the known value into the CCGain and CCDelta parameters in the calibration section of the dataflash.

    Regards,

    Doug