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BQ76920: What's the current CC offset Accuracy?

joy zhou
Intellectual 565 points
Part Number: BQ76920
Other Parts Discussed in Thread: BQ78350, , BQ78350-R1A, BQSTUDIO

Hi，

I have a project based on bq7692000+bq78350. On some of circuit boards,  after current CC offset calibration, current still cannot be 0, it can be keeping as -4mA, or jumping between 0 and -4mA.(-4mA is an example)

Could you please help me to know what the current value range which I can expect after a CC offset calibration?

In the project, we are using a 1mohm current senses resistor. During calibration, LEDs are off, no load. I attached the gg file in case it is needed.

Thanks,

JoyPRG_V0.gg.csv 

  • 0
    TI__Guru* 81035 points

    Hi Joy,

    For the calibration, are you following the steps in Section 12.2.5 of the BQ78350-R1A Technical Reference Manual? Keep in mind that the LSB for the BQ76920 coulomb counter is 8.44 uV, so one LSB of error will result in a few mA of error. 

    Best regards,

    Matt 

  • 0 in reply to Matt Sunna
    Intellectual 565 points

    Hi Matt,

    We did current CC offset calibration through bqStudio, Calibration, Current Offset screen. This time, we got 1400 pcs circuit boards good, but got 14 pcs with the issue: after CC offset calibration, the current jump back and forth like 0 to -4mA.

    I want to know after a successful current CC offset, should the current reading keeping as 0 or can be a little jumping? Please advise.

    Thanks,

    Joy

  • 0 in reply to joy zhou
    TI__Guru* 81035 points

    Hi Joy,

    I think it is not unusual for it to fluctuate by an LSB because the sense resistor with this sense resistor value. You can also take multiple measurements during calibration and take an average (this way you will see both the 0 and -4mA measurements during calibration hopefully). I think BQStudio does an average of multiple measurements already though.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 565 points

    Hi Matt,

    Got it. Thanks!

    I will increase Current Deadband parameter to get stable 0A.

    Thanks,

    Joy