When the primary design goal is a linear amplifier with high CMRR, do not exceed the op amp input common-mode voltage range (V_CM). This CMRR is used to set the common-mode input range specifications in Section 7.5. The typical V_CM specifications for the OPAx607 devices are from the negative rail to 1.1 V below the positive rail. Assuming the op amp is in linear operation, the voltage difference between the input pins is small (ideally 0 V) and the input common-mode voltage can be analyzed at either input pin; the other input pin is assumed to be at the same potential. The voltage at V_IN+ is easy to evaluate. In a noninverting configuration (Figure 8-1) the input signal, V_IN+, must not exceed the V_CM rating. However, in an inverting amplifier configuration, V_IN+ must be connected to the voltage within V_CM. The input signal applied at V_IN- can be any voltage, such that the output voltage swings with a headroom of 10 mV from either of the supply rails.

The input voltage limits have fixed headroom to the power rails and track the power-supply voltages. For single 5-V supply, the linear input voltage range is 0 V to 3.9 V and with a 2.2-V supply this range is 0 V to 1.1 V. The headroom to each power-supply rail is the same in either case: 0 V and 1.1 V. A weak NMOS input pair from V_IN+ to V_IN+ – 1.1 V ensures that an output phase reversal issue does not occur when the V_CM is violated.

Figure 8-4 Internal ESD Structure

The OPAx607 devices also incorporate internal electrostatic discharge (ESD) protection circuits on all pins. For the input and output pins, this protection primarily consists of current-steering diodes connected between the input and power-supply pins. These ESD protection diodes provides input overdrive protection, as long as the current is limited with a series resistor to 10 mA, as stated in Section 7.1. Figure 8-1 shows a series input resistor can be added to the driven input to limit the input current.