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Reading raw coulomb counter values

Stephen Snyder
Prodigy 40 points
Part Number: BQ27421-G1

Hello.

We have a defect at our factory that can cause high current, and we'd like the ability to screen for it after the device is assembled.  Since our device is so low power, for us high current can be an excess of 10 or 100uA.  Since the Coulomb Counter is an integrating ADC, in theory, if we integrate over a long enough time period, we should be able to measure even uA of current.  But I only see the ability to read AverageCurrent() which is in units of mA and is only averaged over 1 second.  I'd like to average over a longer period and have the result in uA, or raw counts such that I can calculate the current.

Is there any ability to read the raw coulomb counter values?  I think additionally we'd need to force it on (I'm not sure if it shuts off sometimes due to low current and uses voltage measurements only).

Any help would be very appreciated.  The ability to measure uA level current in production test could be extremely valuable for many customers.

Thanks!

Steve

  • 0
    TI__Guru** 105590 points

    Hello Steve,

    In theory yes this could work, but the gauge cannot keep oversampling for many seconds, our firmware and hardware is setup to do periods of 1s for coulomb counting. Also with measurements like this noise becomes a large issue and the current read may not be very accurate.

    Most of the time for customers wanting to measure very low current, we recommend using a larger sense resistor and scaling the current calibration of the gauge, for example tell the gauge 100mA is actually 1A for 10x reduction. But since this is an internal sense resistor you will not be able to do this implementation on this gauge platform.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 40 points

    Thanks for your quick reply.

    I understand your concern about the noise.  But if I wanted to just try it anyway, to see how it performed, are there any undocumented commands that could allow me to instantaneously read the contents of the raw coulomb counter?

    Thanks!

  • 0 in reply to Stephen Snyder
    TI__Guru** 105590 points

    Hello Steve,

    Unfortunately all our conversion times are preset in our firmware, there's not a method to extend the sample times.

    Sincerely,

    Wyatt Keller