in order to prevent Psub-nwell diode forward conduct when voltage is negetive , a iso-nmos is used. now the problem is whether two nmos may oxide rupture,
the process has BDVds>12V, but Tox is 150A, so Vgs<5V to avoid oxide rupture.
but for my schematic configuration, Vgs(Vgd) some time exceed 5V.
There is a doubt how can nmos operate when Vds=12V and BDVgd<5V simultaneously?
U have wrong opinion regarding safe operation regions of MOSs in ur process.
BDVgd can be higher than BDVgs for special device structures. Look in PDK docs or ask FAB about.