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BQ76952: BMS triggers OCD1 or SCD when trying to power simple buck-converters and capacitive loads

Mo Mizzi
Intellectual 290 points
Part Number: BQ76952

Tool/software:

We are running into issues with running control boards that have buck-converters, lot of capacitors etc.

We designed a 13S battery using the BQ76952, while the battery seems to be fine on a linear load it's not able to power a capacitive load. It's triggering OCD1 (which is set to 30A, using a 1mR resister) right at power-on. Attached is the schematics for reference.

1538.13S_BatteryPack.pdf

  • 0
    Intellectual 290 points

    I have tried increasing the thresholds of all the protections and also removing them. But the BMS is struggling to power a simple load (we haven't even connected our motors or mother board yet).

    I'm not able to understand what could be restricting the flow of current through the FETs. Is it the FETs limitation ?

    They are rated for 100V, 56A, as shown in the attachment above. It's similar to the reference designs provided under BQ76952.

  • 0 in reply to Mo Mizzi
    Intellectual 290 points

    Good morning,

    Just following up to see if anyone had a chance to look into this issue. Thank you.

  • 0
    TI__Prodigy 730 points

    Hi Mo,

    What is the total capacitive load that the battery is trying to power up? Is there any series resistance to this capacitive load to limit the start-up current (ESR or explicit resistance)?

    Do you have any waveforms showing the current pulled from the battery or the current/voltage of the capacitive load during power-on?
    With a very large capacitive load, the start-up current may be very large and be sustained for a significant amount of time until the capacitive load is charged up.