The inputs of the INA851 device are individually protected for voltages up to ±40 V beyond the power supply rails. For example, a condition of V_S– = –55 V on one input and V_S+ = 55 V on the other input does not cause damage. Internal circuitry on each input provides low series impedance under normal signal conditions. Figure 8-10 shows that if the input is overloaded, the protection circuitry limits the input current to a value of approximately 16 mA.

Figure 8-11 shows that during an input overvoltage condition, current flows through the input protection diodes into the power supplies. If the power supplies are unable to sink current, then place Zener diode clamps (ZD1 and ZD2 in Figure 8-11) on the power supplies to provide a current pathway to ground.

If an input stage gain greater than G_IN = 1 V/V is implemented, where a gain resistor is present across the RG pins, the inputs are still well protected against overvoltage conditions; however, make sure that the input differential voltage limitations of the INA851 are not exceeded. For example, a condition of (V_S+) + 40 V on both inputs does not cause damage. However, a condition of (V_S–) – 40 V on one input and (V_S+) + 40 V on the other input can cause damage. Precautions can include the use of external resistors in series with each of the inputs.