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bq2060a convergence issues

Habib Farahani
Prodigy 110 points
Other Parts Discussed in Thread: BQ2060A

Hello Everyone,

I have a question about fuel gauges, in particular bq2060a.  I am using a bq2060a interfacing with OMAP3 using HDQ interface.  After a few charge and discharge cycles I see a divergence in measured voltage vs. measured charge.  For example, I read 7.6 volts from fuel gauge while remaining capacity shows %1.  The new battery typically maps such voltage with around %30 of remaining capacity.  Is this normal?  What is the best way to make sense of fuel gauge?  It seems that the chip gets out of calibration and cannot converge to a proper value anymore.

Please let me know if you need more info.

 

  • 0
    TI__Genius 10235 points

    What battery chemistry is you pack? It's possible that the VFC was calibrated incorrectly.  Make sure that the measured current is the same as the gauge reported current. It's also possible that the EDV values (or CEDV, depending on your configuration) are incorrect for your particular pack.

  • 0 in reply to Chase7071949597
    Prodigy 110 points

    Hello Chase,

    Thanks for your reply.  The battery pack is Li-Polymer with 50Wh capacity.  I am not sure about the values of VFC since the batteries are being manufactured by a third party.  The problem I see is that initially the batteries seem to be working fine but after a few charge and discharge the divergence occurs.  For example I have several batteries that charge to %86 or %95 percent and that is the maximum they get to.  The voltage indicates full charge but the percent charge is off by a variable amount.  One thing that I did not mention is that we have incorporated a protection circuitry that will cut off the fuel gauge supply (battery) once the voltage falls below a threshold.  This is to guarantee that a cell under voltage doe not happen.  In my testings I have ensured that the protection circuitry has been tripped and therefore, the fuel gauge has been disconnected (reset condition)  Would you think this is a contributing factor?  Is there any way to put the fuel gauge is a recalibrate mode?

    Regards,

  • 0 in reply to Habib Farahani
    TI__Genius 10235 points

    The protection circuitry could be causing the problem if the cut off voltage is too high.  If you are using fixed EDVs, there are 3 voltages correspond to 0%, 3%, and 7% state of charge, roughly.  The battery must be discharged down to the 7% point for an FCC sync to occur.  If this does not ever happen, then the accuracy will gradually degrade. 

    If you are using CEDVs instead, it is quite possible that the parameters were calculated incorrectly for the pack. If you have access to a GG file or the data flash settings, you can check to see which method your pack is using. If bit 4 (starting from 0) is set, then you are using CEDVs.

  • 0 in reply to Chase7071949597
    TI__Genius 10235 points

    I forgot to mention the register.  It is bit 4 in the Pack Configuration register.

  • 0 in reply to Chase7071949597
    Prodigy 110 points

    Hello Chase,

     

    Thanks very much for your recommendations.   Since my interface with the fuel gauge is HDQ, I do not have access to the contents of the EEPROM.  However, the battery manufacturer informed me that they have not calibrated the VFC (your first hint).  The values in EDV(s) are a bit too close to the protection cut off and that could potentially cause the recalibration issues we see.  Thanks very much for your help and I hope with the new cal factors our batteries start working better.