mentions connecting the unused inputs to Vcc or to ground. Can you confirm
whether we need them or not?
The ADG3304 datasheet (page 16) recommends that the inputs of the unused
channels (A or Y) should be tied to
their corresponding VCC rail (VCCA or VCCY) or to GND.
Due to the architecture of this device, it is not necessary to tie both
input/outputs, the input side is sufficient
You can see this implemented in the circuit schematic from UG-225 for one of
our evaluation boards where only the Y7 and Y8 side of the unused channels on
ADG3308 is tied to GND.