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LM3481: Power MOS burn down at Drain

NickSY Huang
Prodigy 250 points
Part Number: LM3481

Hi,

I use LM381 to boost from about +8V (V_CHG_OUT) to +40V and -40V (right side of transformer)

But sometimes my Power MOS might be broken by burn down at Drain

The Power MOS I used is SPR100N03, spec as below. Also my schematic.

Is there any possible reason?

The current through Drain-Source is about 2.6A, and Fosc is about 208kHz

Thanks.

SPR100N03(PR-PAK)-2016.01_T02.pdf

  • 0
    TI__Genius 11215 points

    Hello, 

    Thanks for reaching out. What is the design target for your output current? What is your desired peak current set with the sense resistor? Could you please specify the characteristics of your transformer as well? I'm looking forward for your answer. 

    Kind regards, 

    EM 

  • 0 in reply to EM
    Prodigy 250 points

    Hi EM,

    The output might be mA level for comparators use.

    The current with the sense resistor is about 50mA by measuring.

    The transformer is as below

    https://pdf1.alldatasheet.com/datasheet-pdf/view/947384/WURTH/749196238.html

    Thanks for your help.

  • 0 in reply to NickSY Huang
    TI__Genius 11215 points

    Hello, 

    Thanks for your feedback. When exactly does this damage happen? Is it instantaneous as soon as you turn on your power supply? What is the value of your output caps? Could you please try to capture the waveform at the drain of your FET to see if the RCD clamp is clamping correctly the reflected voltage? If possible, could you please share the schematic of the whole circuit including the output caps and the feedback? I'm looking forward to hearing from you. 

    Kind regards, 

    EM 

  • 0 in reply to EM
    Prodigy 250 points

    Hi EM,

    I'm not sure when damage happen. It seems to be the time turning on power supply, but not every time.

    Some devices may happen, and some may not.

    Here is secondary side schematic.(RCD is not installed)

    Vd waveform as below with VOUT= +/-50V (Flyback secondary output Nps = 1:2), VIN= 12V (heavy-loading), overshoot < 45V 

    (RCD is not installed)

    MOS Burn down picture as below

    Would you think it's Vdrain overshoot issue or EAS issue?

    Thanks.

  • 0 in reply to NickSY Huang
    TI__Genius 11215 points

    Hello, 

    Thanks a lot for sharing this information. I would suggest to populate anyway the RCD clamp to protect the drain of the FET. Can you share the layout of this board? Did you notice if the board was overheating as well? 

    Kind regards, 

    EM

  • 0 in reply to EM
    Prodigy 250 points

    Hi EM

    I'm sorry I can't provide layout file, but here is MOS and LM3481 placement in layout (transformer is on the other side)

    BTW, this board is not overheating yet. 

  • 0 in reply to NickSY Huang
    TI__Genius 11215 points

    Hello, 

    Thanks for sharing this info. Usually we do not recommend to split the power stage on two sides of the PCB. An educated guess could be that in this case  there is a current spike during start up and the transformer goes into saturation. Can you please provide the precise value of your load current at the -/+ 40V output and also at the -/+ 5V? Can you please capture during start up the following signals: Vin, Vout, voltage on the drain of the FET and voltage on the sense resistor (R258)?

    Kind regards, 

    EM