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TPS2490: Hotswap TIMER behavior

Robert Ussery
Prodigy 10 points
Part Number: TPS2490

Tool/software:

I have an implementation of the TPS2490 hotswap controller as shown below:

I've been experiencing failures of the Q2B/Q3B FETs during operation when starting into a short circuit and sometimes when applying a short circuit during operation. In debugging this failure, I've found that the TIMER pin does not behave as I'd expect. Here is a scope trace during one such short circuit fault:

And here's another example where I wasn't probing the GATE signal:

The TIMER signal can be seen to charge to 4V in about 0.5ms exactly as expected, but then it stays at 4V and the GATE signal is not pulled low for some time. This causes the FETs to heat significantly while in constant-power mode, finally exceeding their SOA and failing shorted (where the current increases at the end of the trace).

I've replaced the FETs and reproduced this behavior several times, on several boards, so I'm pretty convinced it's not a damaged TPS2490. Can you help me understand why the TIMER signal reaching 4V is not causing the gate signal to drive low?

Thank you for your help!

  • 0
    TI__Mastermind 39820 points

    Could you please please apply 5V on the EN and perform the start-up into short test again? 

  • 0 in reply to Avishek Pal
    Prodigy 10 points

    Thank you for the reply! 

    I changed the EN pin to actually be 12V (it's sourced from a 12V signal via a resistor divider, so it was easiest to just short the top of the divider). With this change, the TIMER appears to function correctly, and the output FETs do not exceed their SOA and fail:

    Is there a minimum required voltage for V_EN for the TIMER function to work correctly? I'd been using the EN for UVLO and sequencing functions that required keeping its V_EN=1.5V. I'd assumed any voltage over V_EN_L=1.28V would keep the hotswap enabled and operating normally:

    Thank you for the help!

  • +1 in reply to Robert Ussery
    TI__Mastermind 39820 points

    Please make the EN voltage minimum of 2V. 

    Please click on "This resolved my issue" if this post answers your query.