I am having some trouble solving an input protection issue for a design that has to measure the voltage of an input between ~10V two 60V DC via a microcontroller ADC. The issue is the micro may be unpowered but the input could remain anywhere between 10V to 60V. This would cause the ESD protection diodes in the micro to conduct which would be bad.
I have come up with the following circuit that simulates but I'm concerned that the Vgs of M3 is close to the -20V limit. In the circuit VIN can be between 10V and 60V, VCTRL would be from the micro to enable M3 during normal operation. If the micro is unpowered then M5 is turned off because R8 pulls the gate to ground. M4 is used for reverse polarity protection.
Am I way off base with this design?