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[FAQ] Can channel input/output pins on a digital isolator be left floating?
Input pins of unused channels of a digital isolator can be left floating without any concerns on device operation. However, to keep the current consumption low, they are best connected to a logic state that is same as default state of the outputs. The device consumes lower current when in default state.
For example, for the device ISO7741 (without suffix “F”, default HIGH state) you can connect unused channel input pin to its VCC through a pull-up resistor (preferably with 4.7kΩ resistance). For ISO7761F (default LOW state), you can connect the unused channel input pin to its GND.
The output pins of all the unused channels are best left unconnected.
Control input pins (like EN pin) have internal pull-up or pull-down resistors and can be left floating for typical operating conditions, but in noisy environment, leaving these 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 pin to an external pull-up or pull-down resistor (preferably with 4.7kΩ resistance) which drives the pin to a strong state and less immune to noise.
