Click here to purchase the entire book in PDF format. Maximum Differential Input Voltage In theory, there is no connection at all between the two inputs of an operational amplifier. If the difference in voltage between the two inputs of the op amp is excessive (on the order of up to $\pm30$ V) then things inside the op amp break down and current starts to flow between the two inputs. This is bad - and it happens when the difference in the voltages applied to the two inputs is equal to the maxumim differential input voltage.