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BQ34110: Learn FCC Update Limit

Prodigy 245 points

Replies: 25

Views: 773

Part Number: BQ34110

Hello again,

After running multiple logging discharge cycles, I have noticed that FCC never updates itself by more than 256 mAh. In the BQ34110 TRM, it says "FCC cannot be reduced by more than FCC Learn Down or increased by more than FCC Learn Up during any single update cycle". "FCC Learn Down" and "FCC Learn Up" are bolded and italicized, which I assumed meant that they are data flash parameters that can be altered. However, there is no such parameter in BQStudio, and there is no other mention of these parameters elsewhere in the TRM. 

Is it possible to increase the FCC Learn Down/Up limit to greater than 256 mAh? Or, if the parameter has only enough space for a 1-byte number, is there a way to turn off the limit entirely? I am asking this because it is clear that our batteries have a full charge capacity that is significantly lower than the Learned Full Charge Capacity reported by the chip (after fully charging, the RC value is approximately 5 Ah, while the learned FCC is approximately 7.8 Ah). I know that Learned Full Charge Capacity is a data flash parameter that can be changed, but I would rather let the chip measure it automatically, just in case our charger isn't working properly somehow. At the same time, I don't want to have to do 6 or 7 charging and discharging cycles because the Learned FCC can only update 256 mAh at a time.

Thanks again for any advice you can give.

Colin 

  • In reply to Bryan Kahler:

    Hi again Bryan,

    Sorry, I must have missed your previous question. Unfortunately we still have not been able to find the bugs. Our problem is still that the SoC (and related values like TTE) drop significantly (about 27% minimum, 8 minutes TTE)  when the voltage hits the EDV2 value, even though our GPCCEDV report tells us there should be an error of no more than 3%. This happens even after we completely discharge the battery and recharge it to 100% SoC while the chip is connected.

    I have noticed that if we don't charge the SoC all the way to 100%, the SoC/TTE value doesn't drop as much when it hits EDV2. The lower SoC we start our discharge, the less the SoC/TTE value drops. This makes me think think that it might be an issue with the Coulomb counter? Is there any way to check this/fix this? We have already calibrated the current reading, and it is fairly accurate with a maximum error of about 0.15 mA. 

    I apologize again for my delayed response.

    Thanks again for your time,

    Colin

  • In reply to ColinY:

    Hi ColinY,

    To test the coulomb counter, please see section 2.6 of the TRM. Accumulated charge measurement.

    It can be configured to accumulate charge or discharge and may be compared against your external measurements.

    Sincerely,
    Bryan Kahler
  • In reply to Bryan Kahler:

    Hi Bryan,

    Ok that makes sense, I didn't really pay any attention to the accumulated charge measurement. Practically speaking, how would you suggest measuring the accumulated charge externally? Would we charge/discharge it to a constant current and multiply current in/out by time?

    Thanks,
    Colin
  • In reply to ColinY:

    Hi Colin,

    This article may help:

    e2e.ti.com/.../how-accurate-is-your-battery-fuel-gauge-part-2-2


    Sincerely,
    Bryan Kahler
  • In reply to Bryan Kahler:

    The article is very helpful. I will let you know once I am able to test the gauge.

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