I'm a DFAE in Japan. Our customer is designing a schematic with ADN4650 and gives us a question. What should we do when the input pins is unused?
The simplest option is probably to connect Din+ to Vdd1 and Din- to GND1; this will prevent any chattering from the unused input.
If the input is potentially unused but might also be connected to a driver, then a biasing network of pull-up to Vdd1, termination across Din+/Din- and pull-down to GND1 can be used (for default output state of positive differential).