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CSD17577Q3A: Circuit with LM25117PSQE - Multiple MOSFET Failures (Short Circuit)

Dean O'Brien
Prodigy 10 points
Part Number: CSD17577Q3A

Tool/software:

Hello,

I have a design using LM25117PSQE with CSD17577Q3A as the MOSFET devices.

Vin = 24nom 18Vmin

Vout = 12V

iout = 10Amax

On several PCBs I have now seen normal operation for some time, followed by a hard failure with low OFF resistance across Q501, and 24V at Vout when the system is powered.  I have not noted any abnormal activity between the working state and the failure.

Please could someone review and offer advice, we are currently working towards releasing the PCB design for production qtys.

Thanks,

Dean

  • 0
    TI__Mastermind 35600 points

    Hello Dean,

    Thanks for your interest in TI FETs. It sounds like a high side shorted FET failure. Have you looked at the switching waveforms (VGS & VDS). Is there excessive ringing or overshoot on the switch node? A couple observations: (1) using a 30V FET on a 24V input does not leave much margin for voltage spikes/overshoot or higher voltage on the input due to transients and regulation. It may be OK but I'd recommend looking at the switching waveforms to make sure it's not exceeding BVDSS for either FET. (2) there is only 10μF + 0.1μF capacitance on the input. That seems pretty low for the amount of output power (120W). In most applications, there are multiple MLCC input capacitors in parallel. The capacitors must be rated to handle the rms input current which can be estimated as Iout/2 (5A). These should be placed as close as possible to the drain of the high side FET and the source of the low side FET or in this case, the current sense resistor GND. Are any other damaged components such as low side FET or controller?

    Thanks,

    John Wallace

    TI FET Applications

  • 0 in reply to John Wallace1
    TI__Mastermind 35600 points

    Hi Dean,

    Following up to see if your issue has been resolved. Please let me know.

    Thanks,

    John

  • 0 in reply to John Wallace1
    Prodigy 10 points

    Hi John,  

    Thanks for your reply.

    I am hoping to look into this issue more this week, and then I will be able to provide an update.
    I plan to increase the VDS of the FETs in the design ready for the next revision of PCB either way.

  • 0 in reply to Dean O'Brien
    TI__Mastermind 35600 points

    Hi Dean,

    Thanks for the update. Let me know when you have more information.

    Best Regards,

    John

  • 0 in reply to John Wallace1
    TI__Mastermind 35600 points

    Hi Dean,

    Following up again to see if this issue has been resolved or if I can be of any further assistance.

    Thanks,

    John

  • 0 in reply to John Wallace1
    TI__Mastermind 35600 points

    Hi Dean,

    Since I have not received a response I assume your issue has been resolved and will close this thread. Please let me know if I can be of further assistance.

    Thanks,

    John