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!