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TPS54531 24v Start-Up Failure

Zac Blume
Prodigy 240 points
Other Parts Discussed in Thread: TPS54531

Hello,

I'm using the TPS54531 in a design requiring about 4.5A@5VDC (for USB and some other electronics). The problem I'm having is that the TPS54531 literally catches fire or ruptures the housing (and as a result, VIN is always shorted to VOUT afterwards) if I apply 24VDC without pre-charging (slowly ramping) the input voltage.

I have tried both the Webench design, as well as the EVM design. Other things I have tried, to no avail:

-Lower ESR output capacitance (always around 94uF, one electrolytic and two 22uF ceramic)

-SS cap from 0.0082 to 0.01uF

-UVLO on EN pin with resistor divider

-Inductor value of 3.3uH to 6.8uH

-Multiple power supplies

The TPS54531 circuit was completely isolated from the rest of the PCB after the first 2 failures, except 2 0.1uF caps on the output.

Ideas not tested yet:

1. Increase the BOOT capacitor size to 0.22uF

2. Lower ESR input caps

3. Filter cap on the VSENSE input

  • 0
    TI__Guru**** 191445 points
    TPS54531 requires X5R or X7R input capacitors they should be a s close to the IC VIN and GND pins as possible. The EVM does not use any electrolytic capacitors, only ceramic. The compensation required will vary unless you use the exact values and dielectric for the capacitors and the inductor should be the same value.

    You state that if you ramp the input up slowly, the circuit works properly, correct? If you are hot plugging 24 V directly you may get transients in excess of the TPS54531 absolute maximum of 31 V. That is probably your issue.
  • 0 in reply to JohnTucker
    Prodigy 240 points
    The input cap is GRM21BR6YA106KE43L (10uF 35V X5R), paired with a 0.01uF 50V 0402 X7R. Perhaps adding more input capacitance can offset this transient?
  • 0 in reply to JohnTucker
    Prodigy 240 points
    The fix was more input capacitance. I tripled what I had there, noticing that the existing cap was only ~2uF at 24VDC. 3 in parallel solved the problem. Thanks for getting me pointed in the right direction.