I am designing an ADC board for Raspberry Pi using the MCP3004 ADC chip. Please see my circuit below.
This circuit is intended to measure voltages form 0 to 10V, to have overvoltage protection (Vin<=24V), and reverse polarity protection.
According to datasheet BAT54 diode has a voltage drop of 240mV @ If 100uA. When 10V will be applied (Vin) the voltage divider will scale it to ~3V. At this time D2 is blocked (except for leakage current). As Vin will rise D2 will open and the input of op amp will stay close to 3.2V. To supply power to D2, a small 3V LDO will be used. When polarity will be reversed, the non-inverting input will see around -240mV, which is more than Vss-0.3V that is specified in LM358 datasheet, so it should be fine.
Everything went fine in simulation, but will this work in real life? When the polarity will be reversed, will the output of op-amp be stable close to 0V?
I read that op-amps are not happy with capacitive load. MCP3004 is a SAR ADC so it can be approximate as an capacitive load (20pF). For that reason Rx Cx are recommended to be used. My question is: Are they really needed? If yes, based on your experience/knowledge, what will be the optimum values?
Thank you in advance for your answers!