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Original question:

BQ27Z561: Can BQ27Z561 support 0.75m ohm sense resistor?

BQ27Z561-R1: SoC jump to 0 when Temperature rise quickly

Ryan Wang
Expert 5470 points
Part Number: BQ27Z561-R1
Other Parts Discussed in Thread: BQ27Z561, GPCRB

Dear expert,

My BQ27Z561R1 works fine at -10C after RBteak.

But in customer test, Battery is in 100% SoC relax for one hour( no current ),  then their temperature ramp from -10C to 0C within around 1 min.  SoC jump from 100% to 0% suddenly at around -2C(Still  NO any discharge current).

Can BQ27Z561 handle this kind of quick temperature ramp? What parameter can help optimizing this situation?

Thanks

  • 0
    TI__Expert 8245 points

    Hi Ryan,

    There are many factors that could cause this sudden SOC jump. I don't think a temperature ramp would cause this behavior so could you send me your .gg file and a .log file of when this behavior occurs? That way I can look at every register on the device and uncover the cause of this SOC jump.

    Thanks,

    Jackson

  • 0 in reply to Jackson DiGiovanna
    TI__Expert 5470 points

    Jackson,

    Below I attached gg file. TI EVM low temp test at -10C and -15C and customer low temp log.

    TI EVM test result is very good.

    However, in customer board low temp test, you can see in line 74243, FCC jump from 1256 to 0 during relax (0 current) at -8C . In fact , FCC1256 is also very low for 100% SoC at -8 degree compared with my EVM test result. FCC 0 is very abnormal.(RM also jumps to 0)

    NOTE: for customer log, temperature should divide by 10 to get real temperature.

    Could you give me some advice why this happen?

    Honor_BT206_Coslight_ID5532_FC4400mV_TC200mA_DM02.gg.csv

    TI EVM BT206_ID5532-10C_ARB.log

    TI EVM BT206_ID5532-15C.log

    Customer board FCC Low temp jump.xlsx

  • 0 in reply to Ryan Wang
    TI__Expert 8245 points

    Hey Ryan,

    So I reviewed all of the logs you sent over and have a few ideas on what may be causing the FCC to drop to 0 in the customer board.

    When ramping through temperatures, the impedance of the cell will obviously change (especially at low temps) even when in relax mode. One of the conditions for updating RemCap and FCC is that the gauge will recalculate these values every 5 degrees. This is why you see FCC and RemCap changing values and lowering in the log file. This behavior is expected to an extent as seen in the EVM log but dropping to 0 FCC is obviously severe and incorrect.

    What I think may be causing this discrepancy is that if you have load select to Average I Last Run, the IC may have learned a new value for this if you had done any extra testing on either the EVM or customer board. This parameter is used in combination with impedance to predict the capacity left in the cell if you were to discharge at the Avg I Last Run. If the value stored here is high enough and the impedance is low enough, the gauge may think that the second you start discharging at that rate, the cell will be depleted. This is what I expect is resulting in the 0 FCC and 0 RemCap values.

    A solution I recommend is first, re upload the same .srec to both the EVM and customer board and run the same test. I expect the values to match if the same exact .srec is used without any new learned values from previous chg/dsg cycles. Secondly, I am not sure if you have used our GPCRB tweak tool but I would definitely recommend this for any application like this one where accurate gauging at low temperatures is required.

    Thanks,

    Jackson

  • 0 in reply to Jackson DiGiovanna
    TI__Expert 5470 points

    Jackson,

    Thanks a lot for your guidance.

  • 0 in reply to Jackson DiGiovanna
    TI__Expert 5470 points

    Jackson,

    If this issue is due to too big Average I Last Run and Average P Last Run. Can I simply change "Average I Last Run and Average P Last Run" register to avoid this issue?

    Thanks

  • 0 in reply to Ryan Wang
    TI__Expert 8245 points

    Ryan,

    You could do that, but the value will update once you do another chg/dsg cycle since this is a learned parameter. Also there may be other parameters that update like your Ra values that could also affect the SOC behavior. I would just start with two .srec files that contain the exact same values for each parameter.

    Thanks,

    Jackson