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BQ27426: Problem that SOC does not transition at 1% intervals

user4369354
Expert 1220 points
Part Number: BQ27426

Dear Sir,

The attached graph shows the parameter readings of the charging IC and fuel gauge IC when a battery is inserted and charged in our device.

200117_BQ27426_Charge.xlsx
The problem is that the SOC suddenly transitions from 90% to 100%.
This problem occurs when the SOC is around 20% when the battery is inserted.
It did not occur with empty battery (SOC=0%), but I think it may happen.
What causes this problem? Also, please tell us if there are any measures to prevent this problem.

Best regard,
Chiaki Endo

  • 0
    TI__Mastermind 24870 points

    Hello Chiaki-san,

    This is because the FC bit is set. Please run this for another cycle and the issue should be resolved.

  • 0 in reply to Kang Kang
    Expert 1220 points

    Hello Kang-san,

    FC bit rise @124min.
    SOC jump 90% => 100% @106min.
    I think that this problem is NOT due to FC bit.
    Please refer to below attachd data.
    200117_SOC_Charge_2.xlsx

    FC bit rise @124min.
    SOC jump 90% => 100% @106min.
    I think that this problem is NOT due to FC bit.

  • 0 in reply to user4369354
    TI__Mastermind 24870 points

    Hello Chiaki-san,

    I don't think the log data contains enough information. Please provide the gg.csv file.

    The jump does look like FC bit set however.

  • 0 in reply to Kang Kang
    Expert 1220 points

    Hello Kang-san,

    If that is correct, the SOC should jump as soon as the FC bit is set. However, this time the SOC jumped before the FC bit was set.
    I also have questions.

    Question1|What are the conditions for updating the values of FCC and RM?
    Question2|For example, does inserting a battery that has just been discharged under high load affect the remaining battery level measurement?

    I think the problem this time was that the fuel gauge IC started learning incorrectly when it first read the battery, so the SOC jumped to correct the error at the end of charging, but is this correct?
    I think that the SOC jump may occur in the battery state as in Question2 above.

  • 0 in reply to user4369354
    TI__Mastermind 24870 points

    Hello Chiaki-san,

    1. The conditions for RemCap and FCC are as follows:

    A) Temperature change by more than DOD at EOC Delta T

    B) Grid point updates

    C) End of charge

    D) During OCV measurements

    E) Qmax updates

    2. Yes, this will cause high initialization error and I believe you are correct. Just let the battery pack rest and gauge take an OCV measurement. That way the error should go away on the next cycle.

  • 0 in reply to Kang Kang
    Expert 1220 points

    Hello Kang-san,

    Q3:Is it possible to observe the timing of "B) Grid point update" and "D) During OCV measurements"? (Are any flags set?)
    Q4:Is "C) End of charge" the timing when the FC bit is set?

  • 0 in reply to user4369354
    TI__Mastermind 24870 points

    Hello Chiaki-san,

    Q3) Unfortunately, no, those are hard coded into the algorithm. It is necessary for the Impedance Track algorithm for these functional simulation updates. The grid points reference the resistance tables.

    Q4) Yes, you can modify this via the VCT conditions. It is taper current, taper voltage. Those are the two.