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BQ34Z100-G1: What DataFlash parameters affect state estimation at power-up/chip reset?

Kevin Banks
Prodigy 235 points
Part Number: BQ34Z100-G1
Other Parts Discussed in Thread: BQ34Z100, GPCCHEM

I'm trying to fine-tune the settings for a new battery pack. After letting the system discharge overnight, it was down to

13.164 volts FCC=15.014 RC=11.222 SoC=75%

I then power-cycled the unit, which restarted the BQ34Z100-G1 too. The new reported data from the part was

13.192 volts FCC=15.072 RC=9.458 SoC=63%

I cannot keep the BQ34Z100 from being power-cycled, due to the way the hardware is setup.

Which Data Flash settings would be most applicable to trying to get the part to make more consistent initial estimates?

(If I am at XX% and I power-cycle, I would like it to be at least close to XX% when it comes back up).

  • 0
    TI__Guru** 105590 points

    Hello Kevin,

    After a power cycle the gauge will take an OCV to correlate to SOC. If your battery voltage is not relaxed when this occurs or if your chem ID is not a good match you may see the behavior you observed.

    If your battery chemistry is LFP it can also make it harder for the gauge to correlate a voltage to SOC value because the discharge curve is very flat.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 235 points

    When the gauge takes an OCV and computes SoC, which DataFlash parameters are part of that computation?

    The chem ID was set by TI previously, based on characterization data sent in.

    Yes this is a LFP battery with a very flat curve. I am trying to see what settings I can change to improve on the current poor performance.

  • 0 in reply to Kevin Banks
    TI__Guru** 105590 points

    Hello,

    Sorry for the late response.

    There are many parameters used to calculate the SOC value, you can review SLUA450 for more information on some of the impedance track parameters.

    If the chem ID was found a long time ago it may be helpful to re-run the cells to get a RDR (relax-discharge-relax) log to submit to the GPCCHEM tool. This may get a closer matched chem ID for your voltage correlation.

    LFP batteries are more challenging because of their flat voltage curve, If possible I would recommend only powering cycling when the batteries are relaxed .

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 235 points

    To those who may find this thread later - we never were able to fix the issue where the gas gauge always makes a "lowball" estimate at startup.

    This is a side effect of the very flat discharge curve. We WERE successful in getting the gauge to bump it's estimate up to 100% at the end of the next charging cycle.

    In our application, we have no control over the incoming power, so ideas like "only disconnect power when XXX" could not be applied.