Hi Pietro Saltarelli,
ADuM1100 do have the default high output when input side is unpowered, you can find this in the table below:
For ADuM110N, you can assume that when input side is unpowered, ouput side will not receive the carrier waveform, and…
Also Weidong, the ADuM1100/1200 are older generation products. The latest generation is ADuM110N (1-ch) and ADuM120N (2-ch). They are more cost-effective and have better performance and robustness.