I would like to confirm about unused channels of ADN4663/ADN4664.
What is the recommended state of input/output pins? (Open or termination?)
I would recommend not terminating the unused output of the ADN4663. This will save on power consumption. You can also terminate this output, but the power consumption of the ADN4663 will be slightly higher.
The ADN4664 unused input should not be left floating. I would recommend any of these options: