Unlike Bi-FET amplifier designs, the LMC649x does not exhibit phase inversion when an input voltage exceeds the negative supply voltage. Figure 6-1 shows an input voltage exceeding both supplies with no resulting phase inversion on the output.

Figure 6-1 Input Voltage Signal Exceeds the
LMC649x Power Supply Voltages With
No Output Phase Inversion

The LMC649x is a true rail-to-rail input operational amplifier with an input common-mode range that extends beyond either supply rail. When the input common-mode voltage swings to about 3V from the positive rail, some dc specifications, namely offset voltage, can be slightly degraded. Figure 6-2 illustrates the input offset behavior across the entire common-mode range.

Figure 6-2 Input Offset Voltage vs Common-Mode Voltage

The absolute maximum input voltage is 300mV beyond either supply rail at room temperature. Voltages greatly exceeding this absolute maximum rating, as in Figure 6-3, can cause excessive current to flow in or out of the input pins possibly affecting reliability.

Figure 6-3 A ±7.5V Input Signal Greatly Exceeds the 5V Supply in Figure 6-3, Causing No Phase Inversion Due to R_I

Applications that exceed this rating must externally limit the maximum input current to ±5mA with an input resistor (R_I) as shown in Figure 6-4.

Figure 6-4 R_I Input Current Protection for
Voltages Exceeding the Supply Voltages