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Original question:

BQ76930: DSG pin not triggering

BQ76930: DSG fet burnout and 1V gate drive

Noel Binny Abraham
Intellectual 535 points
Part Number: BQ76930
Other Parts Discussed in Thread: BQ78350-R1A, , BQSTUDIO, TIDA-00449

Tool/software:

Hi Team,

As mentioned in our previous thread, we’re facing a recurring issue with the BMS design based on the BQ76930 and BQ78350-R1A.

Initially, we suspected the problem stemmed from insufficient voltage at the REGSRC pin in our 6S Li-ion configuration. We addressed this by providing a direct connection from C10 (25.2V max) to REGSRC and marked the earlier post as resolved. However, the issue has resurfaced with very similar symptoms:

  1. On first-time power-up, the board functions normally—both CHG and DSG pins output around 12V as expected.

  2. During continuous testing, with no faults reported in BQStudio, we observed a failure in one of the boards where the discharge FET burned out under a 2A load. Notably, CHG continues to function correctly on all boards, but DSG behaves abnormally.

  3. After removing the damaged FET, we found a short between the Drain-Source of the FET. The DSG gate drive voltage was also observed to drop significantly, fluctuating between 0.5V and 1V.

The REGSRC voltage during these tests was 23V (maximum) and 18V min. The REGOUT voltage is always at 2.5V in all cases. 
The test was done on a 6S system as mentioned above at a max load of 2A. All the fets are rated for higher currents. We see no reason to why the fets should get damaged. 

We would really appreciate your support in resolving this. I'm happy to share the schematic and Gerber files privately for a detailed review.
Looking forward to your guidance.

Best regards,


Noel Binny Abraham

  • 0
    TI__Mastermind 42060 points

    Hello Noel,

    There are many reasons why the DSG MOSFET could be getting damaged. This thread covers most of them:

    Can you confirm all of these cases? Any transients/oscillations/etc.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Intellectual 535 points

    Hi Luis,

    The Tests were carried out at a load current of around 2A, just to prove functional testing and the fets are rated for much higher currents and voltage. 

    Item 1: Checks out. No issues on this end
    Item 2: Checks out. No issues on this end
    Item 3: Checks out. No issues on this end
    Item 4: We have used the same ciircuit as mentioned in TIDA-00449 (https://www.ti.com/lit/ug/tiduar8c/tiduar8c.pdf) along with the BQ78350-R1A. The gate resistor used is a 10Ohm resistor. 

    I've a few shots from the scope and attaching them below for your reference. I'll share the schematic and the PCB on pvt chat as well for your reference.
    We've used a 10 Ohm Gate resistor.  

    1. The fet does not face any transient spike during turn-on as shown below: (Vgs): 


    2. Fet gate-source starts dropping and goes into continuous oscillation after 10 mins continuous running under no fault condition. The load in this case was set to 1A discharge, and after working well for around 10 mins (12V Vgs), the drive output changed as shown below and as mentioned, no faults were detectted on the BQStudio app and OCD and SCD were set to higher limits:



    All boards on a 6S system has shown the same behaviour on my end. Once this is observed, the IC never drives the gate properly and as per our understanding the IC is permanently getting damaged. We'll replace the IC and check if the same issues are being faced after replacement. 

    Look into this and do let me know if there are anymore troubleshooting that we can do on our end.

    Best Regards,
    Noel Binny Abraham




  • 0 in reply to Noel Binny Abraham
    Intellectual 535 points

    Hi Luis, 

    Did  you get a chance to look into this? 
    Waiting for your response. I've shared the schematic and gerber on chat for your reference.

    Best Regards,
    Noel 

  • 0 in reply to Noel Binny Abraham
    Intellectual 535 points

    Hi Luis,

    Still waiting for your response