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Original question:

WEBENCH® Tools/TPS54360: Hot Plugging Burnout with TPS54360

TPS54360: Shorting Output Cap

Paul Edwards80
Prodigy 60 points
Part Number: TPS54360

I have discovered that I can get a shorting failure in 25VDC ceramic output caps when I am driving a 5v output from a 48 VDC input source...

It appears that disconnecting and connecting the 48VDC can generate voltage pulses on the output caps greater than 25V...

If I replace the Schottky Catch Diode with a TVS I can get rid of the problem but the question is why does it occur?

  • 0
    TI__Mastermind 23845 points
    Hi,

    Yes, it all depends on how fast is the input line transient.
    The spike can couple in through internal parasitics and the inductor parasitic capacitor and goes to the output.
    With the TVS, probably this avalanching effect in the SW node is more damped therefore it is not coupled to the output.

    Try to ramp the 48VDC with a slower rate and schottky diode and see if you still have failures.
    I think the key is to damped the input such that it does not overshoot too .

    Maybe this article would help (Maybe a soft-start at the input supply)
    www.ti.com/.../snva717.pdf

    Thanks
    -Arief
  • 0 in reply to Arief Hernadi
    Prodigy 60 points
    I would like to know ALL conditions that would allow the High-side MOSFET to turn on for 2nsec or more...
    I am seeing 2nsec wide ringing at over 14V peak to peak on the 5VDC output when I switch the 48VDC power on...
    I realize that this could be ground bounce coupling but could it be something in the MOSFET on-chip drive circuit?
  • 0 in reply to Paul Edwards80
    TI__Genius 11040 points
    Hello,

    This will be ringing due to parasitics. The high side MOSFET will not turn on for 2ns. As Arief mentioned, the key is to dampen or clamp any ringing above the absolute maximum rating of the device.

    If you have any additional questions regarding this topic, please feel free to open a new E2E thread.

    Best Regards,
    Katelyn