Hi,
Thanks.
Quickly, diff amp just in simulation to try to measure PMOS voltage drop and estimate RDSon from there. Had diff amp schematic from other circuit with gain of 25 where resistor matching and diff measurement output voltage precision are not vital. It's the PMOS I'm interested in in this simulation but the diff amp result had me puzzled. Am doing sim as am looking for Schottky substitute with lower Vforward and nowhere near as much leakage and saw 'ideal diode' using MOS, seems a suitable substitute as a switch rather than a passive part for blocking reverse voltages on a circuit with three different supply voltages.
I understand that besides doing the maths, replacing a transistor switch with a resistor and obtaining the same Vout and Iout is a valid way of getting an idea of simulated, idealized RDSon?
And, sorry for my ignorance here, I read a little about OA saturation before replying and I still don't understand that part of your answer. Could you explain it in other terms, please? Is sensing 12V - 11V on a 12V supply the reason for the incorrect measurement (OA datasheet says input can go beyond supply rails but isn't fully rail-to-rail out) or the 33mV difference the reason or something else?
Thanks.