# Understanding op-amp common mode voltage range when Vin+ is not equal Vin-

I am using MCP662 op-amp as differential amplifier:

First inputs' signal can vary from 0V to 3V and the second input signal can vary from 1V to 1.4V. MCP662 has common mode voltage range equal 1.7V (Vdd-1.3V). In this circuit Vin+ can exceed 1.7V (for example it is 2V when one input signal is 3V and another is 0). However, common mode voltage (Vin+ + Vin-)/2 will never exceed 1.7V.

Is the Vcm range be violated in this circuit? Can this circuit to be used when both input signals can vary between 0V and 3V?

• If you know the Vcm will never exceed the maximum value, why would it violate it? – Eugene Sh. Aug 10 '15 at 21:07

$V_{OUT} = \frac{2K}{1K} (V_{TOP} - V_{BOTTOM})$ (when balanced)