The ADS8588H features an internal clamp protection circuit (as shown in Figure 7-1) on each of the eight analog input channels, respectively. Use of external protection circuits is recommended as a secondary protection scheme to protect the device. Using external protection devices helps with protection against surges, electrostatic discharge (ESD), and electrical fast transient (EFT) conditions.

The input clamp protection circuit on the ADS8588H allows each analog input to swing up to a maximum voltage of ±15 V. Beyond an input voltage of ±15 V, the input clamp circuit turns on, still operating off the single 5-V supply. Figure 7-2 illustrates a typical current versus voltage characteristic curve for the input clamp. There is no current flow in the clamp circuit for input voltages up to ±15 V. Beyond this voltage, the input clamp circuit turns on.

Figure 7-2 I-V Curve for an Input Clamp Protection Circuit (AVDD = 5 V)

For input voltages above the clamp threshold, make sure that input current never exceeds the absolute maximum rating (see the Absolute Maximum Ratings table) of ±10 mA to prevent any damage to the device. A small series resistor placed in series with the analog inputs, as shown in Figure 7-3, is an effective way to limit the input current. In addition to limiting the input current, this resistor can also provide an antialiasing, low-pass filter when coupled with a capacitor. In order to maintain the dc accuracy of the system, matching the external source impedance on the AIN_nP input pin with an equivalent resistance on the AIN_nGND pin is recommended. This matching helps cancel any additional offset error contributed by the external resistance.

Figure 7-3 Matching Input Resistors on the Analog Inputs of the ADS8588H

The input overvoltage protection clamp on the ADS8588H is intended to control transient excursions on the input pins. Leaving the device in a state such that the clamp circuit is activated for extended periods of time in normal or power-down mode is not recommended because this fault condition can degrade device performance and reliability.