So I’m trying to decide if I should ditch the Schottky diodes (1N5817s) connecting to ground in the analog input stage. This is the pre-stage to the ADCs, and the design is for analog input from 0-5V sensors (automotive). 4 Op-amps for 2 inputs. The second op-amp is a sallen-key filter, which then goes to the ADC input (which is a 0-2.5V ADC), thus the divide-by-2 between stages. The two diodes at the input, one to ground and one to +5v, just provides protection from over voltage and reverse voltage on the analog inputs.

The overvoltage protection is a good idea, as it is reasonable to think someone might accidentally hook up something that is going to Vbat (>12v). Hooking up to something with negative voltage is not very common.. and the most probable cause would be by also having the main power connection backwards. In that case you would have no power on the 5V rail (since there is a diode on the power input), but you could potentially get -5Vs relative to ground on an input pin. That would damage the op-amp even with the limited current input… so yea.. I guess I should keep them there… or just not wire it up backwards. 😉