Hey guys/girls.
I'm using an AD795 opamp (
datasheet) in the following circuit:
The problem is that i'm getting more input offset voltage than I expect. From my newbie understanding of the datasheet, at 25*C i should expect Vos to be 100uV typical, 500uV max, and through a 0-70*C range it is typically within 300uV and within 1000uV max. Is this correct?
Measuring across the inputs of the opamp (Fluke 87V HighZ + HiRes mV) i get 760uV @ 22*C ambient. Measuring across the voltage reference i get 4.999V and at the output i get 4.998V, backing up the 760uV measurement.
I realise the AD795 datasheet only characterises it for a +/-15V supply, but i have tried up to a 20V supply and the offset did not budge at all.
As far as i can tell, bias current shouldn't come into play. I tried loading the output with a 50ohm resistor and there was no change. Freezer spray on the opamp brings it up to 800uV.
I was previously using an OPA735 in the same circuit and the input offset was basically zero, so this has me stumped! (I had to get rid of the OPA735 because the auto zeroing circuitry was injecting noise into the output).
Thanks in advance