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BQ78350-R1: BQ78350 Wrong SOC

Martin Marmsoler1
Prodigy 175 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ78350, BQSTUDIO, GPCCEDV

Hello,

I have a 7s5p LiIon battery where we use your BQ78350 chip. For some reason, the SOC drops almost to zero and stays there, even when no current flows and the cells can relax:

This is the srec file we are using:

1665.BASE_CONF.zip

I found this thread, but it did not help:

https://e2e.ti.com/support/power-management/f/196/t/524346?bq78350-Wrong-State-of-Charge

Why the SOC is wrong, but the cell voltages are ok?

  • 0
    Prodigy 175 points

    This is the file read from the BQ78350 chip. It looks different

    BASE_CONF_ReadFromBQChip.zip

    But I don't know what the meaning is.

  • 0 in reply to Martin Marmsoler1
    TI__Guru* 77283 points

    Hi Martin,

    Can you export the .gg.csv file from BQStudio? This can be done by clicking the 'Export' button on the Data Memory tab. This is much easier to read than the srec file.

    Usually SOC issues can be attributed to using the incorrect ChemID for the battery (this is only used after first powering on the device or after a Reset to initially estimate the capacity) or settings for the CEDV Gauging - this can be either the coefficients that came from the GPCCEDV tool if you have it set for compensated EDV detection, or the Fixed EDV values in data flash if you have it set for Fixed EDV detection.

    Also, a log file (click 'Start Log' in the Registers screen) is always helpful for capturing the behavior. If you can capture the point where the SOC drops, the log file will show what is happening in each of the device registers which will help narrow down the issue.

    Regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 175 points

    Here is the gg file

    SBP06.gg.csv

    Here another:

    sbp37_0Soc.gg.csv

    FixedEDVx, x=1,2,3 changed value.

    When I do a reset of the chip, still thesehigh values are in the Fixed EDV settings, but the SOC is then again correct.

  • +1 in reply to Martin Marmsoler1
    TI__Guru* 77283 points

    Hi Martin,

    Whenever discharge is occurring and the cell voltages cross below the EDV2 value, the SOC will jump down to 7%. When they cross below EDV1, the SOC will jump to 3%. It will go down from there. The fixed EDV values in your gg files are very high (12552mV and 30401mV). The values you are displaying in the above screen image look better.

    If you want the SOC to be accurate, I recommend using compensated EDV. I recommend setting the [EDV_CMP] and [CSYNC] bits in the CEDV Gauging Configuration register. The Gauging section of this app note is very helpful to configure the gauging parameters: https://www.ti.com/lit/an/slua924/slua924.pdf

    I also notice the DOD at EDV2 parameter in your gg files is far from the default value - I recommend resetting this to the default. This was probably updated because the EDV thresholds were being triggered incorrectly.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 175 points

    Hi Mat,

    thank you for the clarification. But what might trigger the change of these parameters from 2580, 2680 and 3100(correct once) to 32, 30401, 12552 (wrong once)?

    Best regards,

    Martin

  • +1 in reply to Martin Marmsoler1
    TI__Guru* 77283 points

    Hi Martin,

    These values cannot change automatically. They could only be changed by writing the wrong values to data flash. How are you writing your data flash settings to the device?

    Regards,

    Matt