• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 163 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS54620: Odd failure observed in TPS54620

Bill Batty
Prodigy 70 points
Part Number: TPS54620

I have been trying to track and debug an extremely odd system failure on a PCIe add in card and after a long frustrating incremental process of debug have determined that at least one of the points of failure is in the power system involving a TPS54620RGYR doing very basic conversion from 12V -> 0.9V.

A captured failure event on the scope looks like the PWRGOOD output on pin 14 goes low for around 100ms (and then returns to a logic '1') but there is zero sign of any obvious cause or any other effect on the output. Current consumed is under 6A, 12Vin is stable without any observable droop or noise of any magnitude. Output power doesn't switch off and is well within the band of 91% - 106% specified by the data sheet. What could make PWRGOOD de-assert for a tenth of a second without any change in power in or power out? My only guess so far is that some kind of noise glitch could theoretically be hitting the SS/TR input on pin 9, but I've yet to measure any such event.

  • 0
    TI__Expert 5318 points

    Hi Bill,

    I can't see on the design but is there a 10k-ohm to 100k-ohm pull up resistor for PWRGD pin? Because this is a open drain pin, you will need that resistor (assuming that you have it connected to a voltage source of 5.5V or less). If not added, that may be the issue. 

    If the design does contain a pull up resistor between values mentioned, then it may be important to look other sources of PWRGD drop like thermal, EN and SS pins.

    You may want to check:

    - SS signal, as if SS pin goes below 1.4V then this will trigger PWRGD to drop. Noise at this pin due to layout could be the issue. 

    - EN signal, if there's any noise close the EN pin/trace, then this could also cause PWRGD to drop. Noise could also be injected through the 12V power supply.

    - Thermal, I'm guessing this is not the case, but if you try the above options and they seem to not be the issue then you may look into the device's temp. It's possible that layout and inductor affect the thermal of the device, and if close to threshold, this could trigger the PWRGD drop.

    Regards,

    Eileen