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BQ76952: Turning off DSG MOSFET causes

Abhijith V Narayan
Intellectual 496 points
Part Number: BQ76952
Other Parts Discussed in Thread: BQSTUDIO, , TIDA-010208

Tool/software:

Hello experts,

I am using a custom designed board with the I2C lines connected to a BQ76952EVM to use bqStudio to communicate with the AFE. The schematic is based on TIDA-010208.

I am facing an issue where, when the DSG_FET is made open while the CHG_FET is closed, the voltage across the Pack+ and Pack- drops to 0. This condition is achieved either by the pack entering a CUV condition or by issuing DSG_PDSG_OFF in bqStudio. In both cases, even though the CHG FET is on/closed, I am not getting any voltage on pack output. In this case the voltage should still be present because there exists a path through the CHG FETs which are ON and the body diode of DSG FETs.

No protections are activated. I am attaching a screenshot from bqStudio below and here you can the commands I have issued in order in the transaction log and see the Pack Pin V and LD Pin V in the read data. Please ignore the DDSG and DCHG temps as these are configured as 0b (just report and don't use for protections).

I am also attaching the .gg config file. The schematic can be shared via internal message if required.

AFE_export.gg.csv

Please assist on debugging this issue.

Many thanks,
Abhijith

  • +1
    TI__Mastermind 18005 points

    Hello Abhijith,

    PACK + Voltage should drop to 0V when the DSG FET is open while the CHG_FET is closed. While CHG current is allowed to flow through the body diode of the DSG FET, DSG current is being blocked from the DSG FET body diode.

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Intellectual 496 points

    Hello Alexis,

    Guess sometimes all you need is someone else to press your reset button. The issue came about from a battery cycler we were using to test the pack. After hitting CUV, when the cycler attempted to charge the pack in CCCV, the protection system on the cycler was kicking in. The logs from the BMS were showing the LDPin and PackPin voltage going to 0 and hence all this silly confusion.

    Tried charging with a normal off the shelf CCCV charger and it was charging alright.

    Anyway, thank you and cheers.