Is the ADuM1250 a drop in replacement for the ADum1251?
In general, yes the ADum1250 will drop right in to replace the ADuM1251. It will not work the other way around though, the ADuM1251 cannot usually drop in for an ADuM1250. The only difference between the ADuM1250 and ADuM1251 is that the ADuM1251 has a unidirectional clock line. The side 1 bidirectional clock line of the ADuM1250 will look slightly different than the signal on the ADuM1251 due to the propagation of low to high signals around the buffer. It will produce about 200ns intermediate levels at 0.9V during a low to high transition, but this should not affect the communications.