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BQ40Z60: A brief excessive charging current after wake-up

Sergey Antsupov
Intellectual 545 points
Part Number: BQ40Z60

My device contains BQ40Z60 with 2s 6Ah battery pack and is in production quite a while. I noticed that after initial battery connection there exists a brief excessive charging current pulse when DC power is first applied to wake the gauge. Charging starts five seconds after DC power application with a one second long excessive pulse, then stops for about 1 second and finally resumes with a normal programmed 3A current. Excess value seems to be device dependent (perhaps due to different calibration constants) and noticed to reach as far as 70% over a normal value. I only was able to make notion of the phenomenon because it rarely briefly triggers overcurrent protection in AC adapter. In all the subsequent DC power applications charging starts normally with no this "probing pre-pulse".

Please let me know if this is an intended behavior or it can be eliminated with fine-tuning?

Regards,

Sergey

  • 0
    TI__Intellectual 2146 points

    Hi Sergey,

    Do you have a log and a .gg.csv file for this behavior?

  • 0 in reply to Albert Anwar
    Intellectual 545 points

    Hi, Albert,

    please find my .gg.csv file attached: GoldenImagePKM_LP8067100LC_v15.gg.csv. As to the log, I attempted several times to catch up with the waking up gauge, but, alas, no success (too slow sampling in BQ Studio). But I will gladly provide any further data within my reach.

    Regards,

    Sergey

  • 0 in reply to Albert Anwar
    Intellectual 545 points

    Hi, Albert,

    I managed to log the event of interest (PreCharge.zip) by setting log period to 1000ms in Preferences. Setting it shorter is to no avail, unless collected data is limited to necessary minimum. Actually log data refers to somewhat different situation: waking up into pre-charge, yet brief and huge overcurrent is still seen before pre-charge starts. Please inform me of the necessary minimum data to be collected and I'll try to log better.

    Regards,

    Sergey

  • 0 in reply to Albert Anwar
    Intellectual 545 points

    Hi, Albert,

    more news on the topic: BQ Studio' data graph gives evidence the gauge is aware of the actual overcurrent, though current controlling variables are Ok:

    WakeUp.tif

    Here are oscilloscope traces of the input voltage (in blue) and PH node voltage (in yellow) during wakeup: PH Node.TIF

    Though there must be lots of Nyquist frequency artefacts in the PH node trace, still it can be suggested that there is no switching during overcurrent event in the input supply. Initial switching waveform looks kind of strange too. Normal switching establishes with the overcurrent end .

    Please take a note that overcurrent also affects pre-charge, as stated in my previous post.

    Is there a way out of the situation?

    Regards,

    Sergey

  • 0 in reply to Albert Anwar
    Intellectual 545 points

    Anyone else can comment on the issue?

  • 0 in reply to Sergey Antsupov
    TI__Expert 8315 points

    Hey Sergey,

    Sorry for the extended delay here. I just took a look at the gg and log file you sent in previous replies and am trying to debug the issue. It is not immediately clear to me what the cause of this issue is and it seems like it may be hardware related so would be able to tell me more about how you are connecting the gauge to the pack or provide a schematic?

    Thanks,

    Jackson

  • 0 in reply to Jackson DiGiovanna
    Intellectual 545 points

    Hi, Jackson,

    glad to hear from you.

    Please find related schematic below.

    Battery Manager.pdf

    Regards, Sergey

  • +1 in reply to Jackson DiGiovanna
    Intellectual 545 points

    Hi, Jackson,

    I think I have finally come to a likely explanation of the phenomenon by trying to trace wake-ups. Below is my theory.

    On wake-up the Charger Current Register is loaded with Max Current Register value. The charger then soft-starts and proceeds in pulse-skipping mode while unloaded. After ~5 seconds CHG and DSG FETs turn ON, and the charger starts attempting to regulate battery current to Max Current instead of regular charging current. With my current settings it often leads to DC-power source overload, followed in different scenarios with 100% duty cycle PWM or/and ACLW alarm. Yet after ~1 second more Charger Current Register is loaded with the correct value and after that the charging proceeds normally.

    By now this scenario is known to apply only on wake-up, and most heavily and regrettably it affects initial stage of pre-charge.

    My Max Current Register = 5A while normal charging current is ~3A. The reason of this remaining unnoticed for some time is somewhat controversial definition of Max Current Register, more detailed depiction of which in this post brought me to my theory. By setting Max Current Register to a lower value I managed to eliminate overloads in DC-power source.

    Thus, I suspect untimely load of Charger Current Register in certain circumstances, although there may exist some parameter, regulating this behavior?

    Regards,

    Sergey

  • 0 in reply to Sergey Antsupov
    Intellectual 545 points

    Since no more feedback received so far, I mark the issue resolved.