I'd like to know how to calculate the maximum propagation delay for a digital isolator when using different supply voltages.
I'm presuming that the device is intended to be able to run with different voltages on the two sides. I've used it this way, and I've seen it used this way. The datasheets, however, don't actually give any ratings or examples of this, other than saying "2.25-V to 5.5-V level translation" in the features column.
The datasheets all supply the prop delay times when VCC1 = VCC2 = 5 V, and when VCC1 = VCC2 = 3.3V, and when VCC1 = VCC2 = 2.5V.
How about when VCC1 = 5 V and VCC2 = 2.5V, for instance?