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BQ27742-G1: SOC drop question

Statham Su
Genius 4990 points
Part Number: BQ27742-G1


Hello Sir:

Our customer use BQ27742 has SOC drop question.

Please refer the figure as below.

I also attached log file and gg.csv for you reference.

Please help us to check how to fix this issue?

Thanks a lot.

SendumRma#1Dsgg1A28V-20210623.xlsx

#1-20210623.gg.csv

  • 0
    Genius 4990 points

    Hello Sir:

    Do you have feedback for us?

    Please let us know your recommendations.

    Thanks a lot. 

  • 0 in reply to Statham Su
    Genius 4990 points

    Hello Sir:

    Can you give us recommendations?

    We need your help.

    Thanks a lot.

  • 0 in reply to Statham Su
    TI__Guru 64266 points

    This looks like the gauge overestimates capacity during discharge with RM (coulomb count and simulations) being much higher than FCC, even close to terminate voltage. When the cell relaxes after discharge, the gauge takes an OCV measurement and recalculates depth of discharge, runs another discharge simulation and this returns zero capacity, hence you get a drop.

    1. Are you sure you use the correct ChemID? How did you obtain this ChemID

    2. Did you run a successful learning cycle?

    3. Did the gauge measure an OCV (was the cell relaxed) prior to discharge?

  • 0 in reply to Dominik Hartl11
    Genius 4990 points

    Hi Dominik:

    We will try to reselected the ChemID and golden learning.

    But we have some doubts, can you teach us how do define "gauge overestimates capacity during discharge with RM (coulomb count and simulations) being much higher than FCC" ?

    We cannot understand how do define it, cause according the discharging time and current that sum of mAh decreased calculation was about 2548.4mAh.

    When discharging current was stopped that RM was 1875mAh, and initial RM 4484mAh - 2548.4mAh= 1935.6mAh.

    And I think that 1935.6mAh is almost equal 1875mAh.

    Did you means that RM has problem or FCC has problem?

    Can you provide more explain for us?

    Thanks a lot.

  • 0 in reply to Statham Su
    TI__Guru 64266 points

    The gauge will calculate FCC based on charge termination conditions (taper current/rate and V at Chg Term), load prediction configuration (load select and load mode) and terminate voltage settings by simulating a discharge using a model of the cell described by the ChemID.

    For this to work accurately, you'll have to make sure that the ChemID is compatible, that the gauge learned QMax and Ra (=successful learning cycle), that the charge termination settings are correct (and that the gauge measured V at Chg Term after detecting a full charge) and that the load prediction is compatible with your application (default settings usually work).

    It will also calculate RM based on an OCV (open circuit voltage) measurement for a particular cell and scenario, run a discharge simulation from the depth of discharge based on this OCV down to terminate voltage using load prediction and then start to coulomb count. It will perform additional discharge simulations while discharging to correct for any changes in conditions that require an adjustment to coulomb count.

    Along the line, somehow your RM is way too high when cell voltage reaches terminate voltage. That's why I said that the gauge overestimated capacity.

  • 0 in reply to Dominik Hartl11
    Genius 4990 points

    Hi Dominik:

    We follow your recommendations to select a new Chem ID and relearning again.

    Please refer the GPC report and Golden GG and Learning log as attached file.

    27742 Golden GG and Learning log.rar

    Please help us to check this Golden GG file and learning log were successful or not good enough?

    Please provide your recommendations for us.

    The other we already used this Golden GG file to do testing but got bad results.

    That SOC still has drop condition please refer below file.

    SP300.rar

    It's for you reference tested results.

    Thanks a lot.

  • 0
    TI__Guru 64266 points

    The log file looks like somehow the gauge is reset frequently. DOD at EOC should not change that often and there are many errors in the status column.

    I recommend checking the HW setup to make sure that the gauge is powered up stably. Measure REG25 during the test and set a scope trigger to capture REG25 if it falls below 2.3V

  • 0 in reply to Dominik Hartl11
    Genius 4990 points

    Hi Dominik:

    Can you teach us how to check the reset condition on the log file?
    Please help to high light it for us.
    And we will try to measure the REG25 voltage and update for you soon.
    Thanks a lot.

  • 0 in reply to Statham Su
    TI__Guru 64266 points

    There is no direct check for reset from the log file. However, the log file shows that communication failed (there are an enormous amount of status errors and corrupt results in general) and there are several updates to parameters that will not update during regular operation, hence it looks like somehow the gauge was periodically reset. If you didn't send the reset command, then this could be due to watchdog timer or something is not working correctly on the electrical side (hence it's important to check REG25).