Hello,
OPA197 datasheet only appears to specify input offset voltage (Vos) at 25deg.C.
Please advise Vos spec. between 0deg.C to 85deg.C as well as at -20deg.C for operation at Vs = +/-18V across the entire common mode voltage range.
Does Vos increase or decrease with temperature?
Regards,
Nitish Agrawal
As you may see from the Vos and drift distribution below, Vos may either be positve or negative.
Most of the datasheet specification limits are set by 4-sigma distribution. Thus, in order to calculate the maximum (4-sigma) input offset voltage, Vos_total, across -20C to 85C temp range and common-mode voltage range, you must add different components of Vos_total: Vos(@25C), drift and CMRR Vos error. And since they are all uncorrelated (may shift in different directions), you must add them as a vector quantities (square-root of squares).
For Vcm < (V+)-3V
Max Vos(@25C) = +/-100uV
Max Vos drift =+/-2.5uV/C so max change in Vos due to drift is (85-25C)*2.5uV/C = +/-150uV
CMRR=ΔVcm/ΔVos_cm=110dB (3.16uV/V) so ΔVos_cm=9V*3.16uV/V = +/-28.6uV (max ΔVcm from mid-supply on +/-18V is 9V)
Therefore, the maximum Vos_total=+/-√(100^2+150^2+28.5^2) = +/-√(33312) = +/-183uV
