8.3.5 Input Protection

The INA827 inputs are individually protected for voltages up to ±40 V. For example, a condition of –40 V on one input and +40 V on the other input does not cause damage. However, if the input voltage exceeds [(V–) – 2 V] and the signal source current drive capability exceeds 3.5 mA, the output voltage switches to the opposite polarity; see Figure 14. This polarity reversal can easily be avoided by adding a 10-kΩ resistance in series with both inputs.

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 safe value of approximately 8 mA. Figure 14 illustrates this input current limit behavior. The inputs are protected even if the power supplies are disconnected or turned off.