Hi all and thanks in advance for your help. I am using an op amp MCP607 connected as a voltage follower (with negative feedback). Vdd is 5.0V and Vss is connected to ground. When I pass 1V to (+)input I get 1V on the output, which is normal. But If i pass 3.5V to (+)input I get 3.53V on the output, - well probably ok, and if I pass 4.5V to (+)input I get 5V on the output. This is very strange to me. This opamp has a 120dB Open loop gain and a 250uV input offset voltage. Having read the article on op amps , I would expect to have a slightly lower voltage, say with a couple of mV, but not 0.5V. What could be wrong?