Part of a PCB I designed looks like this:
Simple phototransistor with a resistor to measure the voltage over. More light => more voltage over the resistor.
However, the circuit behind the output doesn't like it when the impedance of it's input is too high. Lacking a better idea, I decided to try what effect an opamp as isolation buffer would have:
The opamp (LM358N) got hot and didn't perform as expected.
VDD is 3.3V, not even close to the maximum Vin the LM358 is rated for.
Did I cut a corner I shouldn't have cut or did I make a seriously stupid mistake here?
To avoid any confusion: the circuit without opamp works exactly as intended. Just not in combination with the next stage of the design.