The inputs of the PGA849 are individually protected for voltages up to ±40V beyond either supply. For example, an input common-mode voltage anywhere between –55V and +55V does not cause damage when powered from ±15V supplies. Internal circuitry on each input provides low series impedance under normal signal conditions, thus maintaining high performance under normal operating conditions. If the input is overloaded, the protection circuitry limits the input current to a value of approximately 4.8mA. Figure 7-2 shows the input protection functionality during an overvoltage condition.

Figure 7-2 Input Current vs Input Overvoltage

Figure 7-3 shows that during an input overvoltage condition, current flows through the input protection diodes into the power supplies. In applications where the power supplies are unable to sink current, place Zener diode clamps (ZD1 and ZD2) on the power supplies to provide a current pathway to ground.

Figure 7-3 Input Current Path During an Overvoltage Condition