He is powering from a bench supply with proper decoupling. With the inputs floating the customer sees a level of 850mVdc on OUT and a 50mVpp oscillation. With the inputs shorted a customer sees it go down to 650mVdc. What should be the correct output voltage with floating pins or zero-difference between the pins? When he adds a cap on the output, the oscillation goes away, but could the additional cap be avoided as per some figures in the datasheet which do not add the cap? Can something be done with the Offset feature to help?
His application will be to measure around 500kHz from 500mW to 100W. I suggested he terminate the source properly and AC-couple to the input and put a 1nF cap on the output.