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BQ27542-G1: Correcting an Inaccurate Gauge

Craig Carder1
Intellectual 510 points
Part Number: BQ27542-G1

Hello,

       I'm working with the bq27542-G1 in a custom design and the SOC values are inaccurate.  A golden pack was created initially and the gauge values were fine.  We are unsure why the gauge is inaccurate now but we wanted to know if there were a way to correct the gauge in the field.  Our MCU is connected to the gauge via I2C.  Is there a command we can send to re-calibrate the gauge.  We don't have control over the current since it is in a device so we can't calibrate with open circuit or anything like that.  

       What we are currently seeing is a SOC anywhere from 25%-37% with a battery voltage of around 3.3V.  Based on our current draw, we expect this to be around 7 - 13% SOC.  Is there anything we can do to tweak the gauge on the fly?

Thanks

Craig

  • 0
    TI__Guru* 76230 points
    hello Craig,
    You should get the gauge to have a qmax update. To do so, read the qmax of the gauge, charge the battery to full, let it relax for 2 hours, discharge atleast 50% and let it relax fro 5 hours. Read the qmax again to see if it change. If it did, then accuracy should be restored. If it didn't then repeat the test, but this time discharge to empty and then rest for 5 hours. You may need to do this several time if you never had relaxation periods that allowed qmax to update while in use.
    Also, you should realize that you can't use voltage correlation to SOC for an aged battery. The IR drop due to the increased internal impedance of your battery will make your correlation wrong.

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 510 points
    Hi Onyx,

    Can you explain the auto-calibration function? Is this something we could try? We are still seeing inaccuracies in the gauge.


    Thanks

    Craig
  • 0 in reply to Craig Carder1
    TI__Guru* 76230 points
    Hi Craig
    Can you elaborate on what kind of inaccuracies you are seeing with the gauge. Is i current measurement accuracy or is the SOC measurement inaccurate? Auto calibration is controlled by the gauge and not by the user. Pls see the technical reference manual of the gauge
    thanks
    Onyx