I've spent this evening blowing up TPS54231s. Even a couple of TPS54331s.
(note that C31 is currently DNP)
The input voltage is specified as 17-24 VDC, and this circuit's worked admirably well at 17 volts for a couple weeks now. This evening I've been testing it at 24 volts. With an adjustable bench supply (not a fantastic one - it's a surplus laptop power supply and a Chinese eBay adjustable buck converter), it works ok at 24 volts (to be fair, however, at startup the source supply is drooping a tiny bit, so it may not be a fantastic test of maximum voltage capability).
The trouble starts when I plug in a 24 volt surplus laptop power supply. The TPS54231s instantly die and short out the input. Now, I admit I haven't tried to characterize this input supply's startup characteristics by capturing it on my scope. I'm starting to run low on replacement chips and I'm done with that for now. But the steady-state voltage is correct under load and not - 24V. The TPS54231's absolute maximum input voltage is 30V. Could it be at all likely that the input supply is spiking beyond that - however briefly - and that's toasting these chips?
Assuming that's true, would replacing the S1M with a 24V TVS diode solve the problem?
I really don't want to reduce the input supply voltage spec.