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BQ27530-G1: Full Charge Capacity Smooth Update issue(result in SOH dip from 100%)

Mythili Balakrishnan
Prodigy 190 points
Part Number: BQ27530-G1
Other Parts Discussed in Thread: BQSTUDIO, GPCCHEM

Hi TI Team,

We have successfully completed learning cycle in BQSTUDIO for BQ27530 part with respect to our battery(3000mAH)

We are facing issue in Full charge Capacity Smooth update, sometimes it is updating properly as ~3000mAH whereas not always.

Full charge capacity Smooth is updated as ~2000mAH which result in SOH dip and battery percentage is also not predicting properly but Full charge Capacity true is predicting properly always

Please let us know what could be the reason for this issue and also attaching .gg file for your reference

6545.Data_flash.gg.csv

Warm Regards,

Mythili B

  • 0
    TI__Guru 52906 points

    The gg file doesn't contain enough information to analyze this behavior.

    Is there anything during your test or use case which correlates with this significant drop in FCC? For example, does temperature change significantly or does charging stop at a lower voltage or is there a significantly higher load?

  • 0 in reply to Dominik Hartl11
    Prodigy 190 points

    Hi Dominik,

    Temperature, Charging and load everything looks to be fine.

    When I insert the battery sometimes it's SOH is dropped to 72% when I remove the battery and connect it back SOH is updated too 100%(FCC also updated properly)

    Is there any specific reason for this behavior of Fuel Gauge

    Warm Regards,

    Mythili B

  • 0 in reply to Mythili Balakrishnan
    TI__Guru 52906 points

    If this large difference happens upon pack insertion, chances are that the pack data is significantly different for pack0 and pack1.Your gg file shows a significand difference for Qmax Cell 0 and Qmax Cell 1. Cell 1 has a cycle count of 1. Cell 0 has a cycle count of 0. Did you run a learning cycle? Qmax Cell 1 looks incorrect (1544mAh for a 3000mAh Design Capacity cell).

  • 0 in reply to Dominik Hartl11
    Prodigy 190 points

    Hi Dominik,

    We are using single cell lithium ion battery in our application. So, when we ran learning cycle only Cell 0 values were updated & for Cell1 default values were retained.

    Also, as per .gg file, cycle count for Cell 1 is zero and for Cell 0 it is 4.

    Please let us know whether Cell 1 parameters needs to be updated same as that Cell 0

    Warm Regards,

    Mythili B

  • 0 in reply to Mythili Balakrishnan
    TI__Guru 52906 points

    Both Cell 1 and Cell 0 parameters must match the cells that you use. The reason why you get different results is because the gauge can't reliably detect which cell you use based on resistance measurements.

    The main problem then is, why did the gauge measure 1544mAh Qmax for a 3000mAh cell? Something is seriously wrong (either incompatible ChemID or damaged cell) if the gauge measures Qmax that low.

  • 0 in reply to Dominik Hartl11
    Prodigy 190 points

    Hi Dominik,

    We got CHEMID from GPCCHEM tool, it is proper with DOD deviation less than 3%

    When we ran learning cycle only for Cell 0 the matching values were updated automatically whereas for Cell 1 the default values were retained.

     In BQ27530 datasheet, the default flash parameters were mentioned(refer the image below)

    The value 1544mAH for Cell 1 Qmax is not updated because of learning cycle, the value 1544mAH is default one so it is retained

    Since we are using single cell battery we checked the parameters for Cell 0 alone, Is it necessary to update the same parameters for Cell 1 also even though it is single cell application

    Please provide your thoughts on this

    Warm Regards,

    Mythili B

  • 0 in reply to Mythili Balakrishnan
    TI__Guru 52906 points

    Did you manually update Qmax Cell 0? Because that one looks correct for a 3000mAh cell.

    I recommend to manually copy Qmax Cell 0 to Qmax Cell 1 and also copy the learned Ra data (the one that's not default) so that both cell configurations match.

  • 0 in reply to Dominik Hartl11
    Prodigy 190 points

    Hi Dominik,

    Dominik Hartl11 said:
    Did you manually update Qmax Cell 0? Because that one looks correct for a 3000mAh cell.

    No, QMAX for Cell 0 is updated automatically when we ran learning cycle

    Dominik Hartl11 said:
    I recommend to manually copy Qmax Cell 0 to Qmax Cell 1 and also copy the learned Ra data (the one that's not default) so that both cell configurations match.

    Manually, I have copied the QMAX and Ra data for Cell 1. But still I am could able to see SOH dip

    When we connect battery first, then power through USB nowhere I found SOH dip whereas first when I connect USB then battery, SOH dip is observed(from 100% to 72%)

    SOH dip is coming because FCC_Smooth value is not updated properly(~2000mAH)

    FCC_TRUE value at the start it was around 2000mAH but within few seconds it is updated to ~3000mAH

    Is this scenario expected one?

    Even when FCC_Smooth value is updated to ~3000mAH after full charge cycle , SOH still remains the same, So please let us know how can we increase SOH back to 100% & will SOH dip create any impact in battery percentage prediction

    Warm Regards,

    Mythili B

  • 0 in reply to Mythili Balakrishnan
    TI__Guru 52906 points

    True FCC will only update if there's a state change (e.g. charge to relax or relax to discharge etc.) or if there's a temperature change or if the gauge detects a cell.

    SOH will not affect SOC prediction. It's just a ratio of FCC and DesignCapacity.

    The only way to debug this is if you log the registers from the gauge over time while running your experiments. Your description is too sparse for me to understand what's happening in your system. 

  • 0 in reply to Dominik Hartl11
    Prodigy 190 points

    Hi Dominik,

    Our product will be getting power from either USB or battery.

    Below are the few observations

    1) When I connect USB alone(without battery), FCC_Smooth value shown in BQSTUDIO is 1583mAH(refer the image below)

    2) After connecting USB when I insert battery, FCC_Smooth value shown in BQSTUDIO is 2113mAH(refer the image below), here FCC_TRUE will be updated to the matching capacity after sometime but FCC_Smooth still remains at lower capacity

    3)When I insert battery first, FCC_Smooth value shown in BQSTUDIO is 3159mAH which is almost matching with our battery spec(3000mAH)


    What is the reason for wrong FCC value update when battery not connected, how can we avoid this SOH dip

    Warm Regards,

    Mythili B

     

  • 0 in reply to Mythili Balakrishnan
    TI__Guru 52906 points

    Temperature shows -41 deg.C in your USB powered use case (because there is no temperature sensor attached, I assume). This is what causes the drop in FCC. The gauge should not gauge anything if there isn't a cell attached.

  • 0 in reply to Dominik Hartl11
    Prodigy 190 points

    Hi Dominik,

    Please let us know what could be the reason for wrong temperature prediction when battery is not there & how can we get rid of this wrong temperature issue

    Warm Regards,

    Mythili B

  • 0 in reply to Mythili Balakrishnan
    TI__Guru 52906 points

    It's not a prediction. It's a measurement. This depends on the temperature measurement selection. You can control this with OpConfig[TEMPS]. See 6.2.14, TRM. Also make sure that the gauge detects a battery correctly. It should not detect a battery if none is connected. Your -41deg.C probably means that you informed the gauge that a battery is inserted and if you selected external temperature measurement with TEMPS, then the non-existing thermistor is super high impedance, causing extreme negative temperature. Check BAT_DET AND BIE (TRM, Table 6-4).