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LM5576: Circuit working fine below 50V, IC burning over 50V

Jamie Ahmed
Prodigy 20 points
Part Number: LM5576

Hello -

I am having some problems with the LM5576 in a custom power supply. I have replicated the circuit from the LM5576EVAL board. The circuit works as expected with one setup, which has a nominal input voltage of 42V. However, in another setup, which has a nominal voltage of 54V, the IC is visibly getting damaged (spark/small flame, magic smoke). This has occurred over several boards (more than I'd care to admit) so it was not an aberration with one IC or board. Please help as this is causing us some pain at the moment!

Please find attached a circuit diagram as well as a photo of a burned-up IC in case this provides some insight.

Thanks very much in advance for any help/insight.

Best Regards,

Jamie Ahmed

  • 0
    TI__Genius 10720 points

    Hello Jamie,

    I have a few questions:

    When do you see the damage occur during your 54V setup? Does it happen as soon as you apply power to the device?

    If you probe the input voltage pin of the IC right when you apply power what do you see?

    Can you please share your layout as well.

    Thanks,

    Harrison Overturf

  • 0 in reply to Harrison Overturf
    Prodigy 20 points

    Hello Harrison -

    Thanks for your response. The damage occurs as soon as power is applied to the device. I have applied power directly from a battery (54.1V) as well as a benchtop power supply configured for 55V @ 15A. I can get a probe of the input next time I test a unit (tomorrow most likely).

    Layout:

    Best Regards,

    Jamie Ahmed

  • 0 in reply to Jamie Ahmed
    TI__Genius 10720 points

    Hello Jamie,

    From what you're describing I believe this damage that you're experiencing may be due to large input voltage transients occurring when power is applied to the input. Using long wires to connect the battery to the power supply can lead to this behavior because the inductance of the lines will form a resonant LC tank with the input capacitors leading to large voltage spikes becoming present at the VIN pin at turn on.

    If you notice a large transient spike present when you probe the VIN pin, you can reduce the peak of the spike using an electrolytic capacitor (on the order of 10uF) with a moderate ESR (on the order of 10mOhm-100mOhm or something close) in parallel with the input capacitors. Ensure that the chosen electrolytic capacitor has a voltage rating of 100V or more to handle the potential spikes.

    Let me know if this helps or not!

    Regards,

    Harrison Overturf

  • 0 in reply to Harrison Overturf
    TI__Genius 10720 points

    Hello Jaime,

    Since I haven't heard back from you, I assume the problem has been resolved. Please post a follow-up question if this is not the case.

    Regards,

    Harrison Overturf