In CMOS if you exceed ~ 1 diode drop beyond either supply rail, you can trigger
a parasitic SCR internal to CMOS structure, that in turn shorts internally the
supply rails and usually blows open the bond wires for Vcc/Vdd and Vss.
https://en.wikipedia.org/wiki/Latch-upIf the SCR not triggered you can still damage the parasitic diode internal to CMOS
with excess current, depends on the source that is driving the pin, eg. its current
capability.
You can add external schottky diodes at pin, and a series R to pin from source voltage being
measured to protect against over voltage, and excessive loading of OpAmp output.
Or a voltage divider to scale the input. Note if you add series R that may effect A/D
conversion settling time for its input sampler, so be aware of speed you run it at.
Some methods of offsetting inputs.
https://www.dropbox.com/s/k1yn4m7heaixvmg/ADinput%20negative%20inputs.zip?dl=0Regards, Dana.