POR may seem simple but simple POR designs tend to
bring you a lot of "customer interaction". Sound like fun?
"POK" (PGOOD) functions will include the POR term plus
under and overvoltage comprisons. A timeout can be a
good feature for rails which see harsh transients, where
you don't want to tip the boat over every time the load
hits or dumps.
POR that looks only at input supply dV/dt, embeds some
dependencies such as a min ramp rate and probably a
"memory" that will drive your test engineer mad (every
test then needs a "quiet dwell" long enough to fully
reset (or adequately at least) the RC network so that
normal operation (not pre-pumped, possibly failing to
put out a reset entirely) is had. I like a DC level check
on the input supply, made as simple as possible and
working at as low an input as possible, in addition to
more sophisticated (accurate) level checks that
happen under a sufficiently high VIN POR maintains proper
reset level through a segue of region-transitions until
proper release point is hit.