The AD823 uses parasitic Schottky diodes to divert the energy due to an ESD
These ESD diodes can protect the IC from ESD hits up to about 1.5kV and can
carry about 10mA of current without blowing. These ESD protection diodes will
act to clamp the voltage at any pin to within 0.5V of the supplies. ESD
protection diodes can carry quite high currents but only for a short period of
time so they can protect the IC from large pulses of short duration (the total
energy is still quite low). The maximum DC current which these protection
diodes can carry is 10mA. Therefore unless you can guarantee that the current
into in pin will me less then 10mA you need some kind of external protection.
External protection could be as simple as a series resistor to limit the
current into a pin. For example if the maximum overvoltage voltage applied to a
pin will be 5V you need to add a 500Ohm series resistor in each digital line to
limit the current to <10mA. The higher you can make this series resistance the
You need to take extra care when designing input protection circuitry for FET
Check app notes AN202 and AN397 for more info.