[FAQ] Can unused channel pins on a digital isolator be left floating?

Input pins of unused channels of a digital isolator can be left floating for testing purposes, but in application leaving the unused pins floating could make the product less immune to noise. The floating pins are especially prone to noise pick-up when the system is subjected to EMC/Immunity tests. To make the system immune to such noise, it is best to tie the channel input to their respective default logic states.

For example, for the device ISO7761 (without suffix “F”, default HIGH state) it is recommended to connect unused signal input pin to its VCC through a pull-up resistor (preferably with 4.7kΩ resistance). For ISO7761F (default LOW state), it is recommended to connect the unused signal input pin to its GND.

The output pins of all the unused channels are best left unconnected.