2402 C grade can not support 75MHz square waveform.
242 we tested is okay. Could you help us to explain the relationships between bps and Hz? Thank you very much.
Actually "bps" stands for "bits per second", and "HZ" is "cycles per second". Here is a simple draft below that could explain.
For ADuM2402 C grade, the maximum data rate is 120Mbps(typical), so it could not support a 75MHz square wave(150Mbps) input. But the ADuM242 could support up to 150Mbps guaranteed data rate.