I don't see any explicit affirmation in the datasheet that VDD1 and VDD2 are completely independent.
I tried VDD1=3.3V, VDD2=5V on the bench and everything seemed fine. But in our application both VDD1 and VDD2 are not set in stone and might change later. Most likely VDD1=1.8V and VDD2 somewhere between 3 to 5V (referred to two different grounds obviously). But I can't anticipate every possible scenario. Can I safely assume that:
Paax: Any combination of VDD1 and VDD2 (1.7 to 5.5V) will work.
The ADuM160N datasheet has an Theory of Operations section which I have circled below and states that:
Internal regulators and input/output design techniques allow logic and supply voltages over a wide range from 1.7 V to 5.5 V, offering voltage translation of 1.8 V, 2.5 V, 3.3 V, and 5 V logic.
The block diagram attached shows that there is transformer isolation from side 1 to side 2, and that GND1 and GND2 are have galvanic isolation by the transformer.
Mea culpa I did not RTFD (read the fabulous datasheet) closely enough. Thanks