I am trying to simulate AD8220 in a very simple configuration. G=1 (no resistor connected), single input supply of 5V and REF connected to ground. Is this a legitimate way to use this component? For input levels below 100mV (ie IN+ = 100mV, IN- = 0) the output has an offset of nearly 250 mV and after 300 mV input the output start tracking input with a smaller offset. This doesn't seem to happen if I add an offset with REF = 600 mV. Any idea what I am doing wrong?