SMPSU IC explosion... (UC3844)

Random failure of the weekend was a UC3844 IC in a switchmode power supply - with a very loud bang, the entire top of the chip blew off, but there's no *obvious* sign of any other failure within the supply. This was one of two such supplies in a Sun RAID disk controller; the two do current-sharing under normal conditions - but the unit will run on one supply if the other fails, which is exactly what happened here. Leads me to *tentatively* say that the RAID unit itself is 100% and the failure was totally in the PSU. So, given that assumption for now, anyone know of a likely fault in a typical SMPSU that might cause such a catastrophic chip failure but no other obvious damage? Seems like a strange one to me, but I assume that something else in the supply has failed and the chip just couldn't handle it. Whilst knowing a bit of SMPSU theory (and practice), I'm not familiar with the UC3844... Of course maybe it was just time for that chip to die (it was at startup, and this in a server which had probably only been power cycled a handful of times in its life), but it sure was noisy about it. Shame Sun don't publish schematics! cheers Jules