The inputs of the INA823 device are individually protected for voltages up to ±60 V and for short transients up to ±80 V. For example, a condition of –60 V on one input and +60 V on the other input does not cause damage. Internal circuitry on each input provides low series impedance under normal signal conditions. If the input is overloaded, the protection circuitry limits the input current to a value of approximately 4 mA.

During an input overvoltage condition, current flows through the input protection diodes into the power supplies, as shown in Figure 8-7. If the power supplies are unable to sink current, then Zener diode clamps (ZD1 and ZD2 in Figure 8-7) must be placed on the power supplies to provide a current pathway to ground. Figure 8-8 shows the input current for input voltages from –80 V to +80 V when the INA823 is powered by ±15-V supplies.