The ADS981x features an internal clamp protection circuit on each of the eight analog input channels, see Figure 6-1. The input clamp protection circuit allows each analog input to swing up to a maximum voltage of ±18 V. Beyond an input voltage of ±18 V, the input clamp circuit turns on and still operates from the single 5-V supply. Figure 6-2 shows a typical current versus voltage characteristic curve for the input clamp.

For input voltages above the clamp threshold, make sure that the input current never exceeds ±10 mA. A resistor placed in series with the analog inputs is an effective way to limit the input current. In addition to limiting the input current, the series resistor can also provide an antialiasing, low-pass filter (LPF) when coupled with a capacitor. Matching the external source impedance on the AINxP and AINxM pins cancels any additional offset error.

Figure 6-2 Input Protection Clamp Profile, Input Clamp Current vs Source Voltage