QIs there a limit to the input current of the AD603, or is the 100 ohm input
resistance, sufficient for most purposes.
AThe input resistance of 100ohm is the differential resistance between pins 3
and 4. It’s the combined resistance looking into the attenuator ladder network.
The absolute maximum ratings on page 3 of the datasheet must be respected at
all times (including power up and power down). The maximum peak input is +/-2V
but the spec also allows VINP to go to either rail for a maximum of 10ms under
There is no explicit current limiting circuit on the input of INP and there is
no extra input protection circuitry therefore the maximum allowed input current
is just 2/100 = 20mA.
If you expect an over voltage condition to occur at the input, during a fault
condition for example, you will need to add in external input protection