I'd like to save power on my 3V3 rail and let the DCDC converter inside ADM2587, pin 8 to run form 5V while RxD supply, pin 2 on CPU level 3.3V. Is such split possible?
Measurements on chip show no connection between VCC pins 2 and 8. I've tried on bench to run the chip in this configuration and it seems to operate properly, but of course I have no glue about long-term reliability. Could you provide me such data?
On the ADM2587E, there is no internal connection between Pin 2 and Pin 8. Pin 2 is the supply pin for the logic portion of the isolator, and Pin 8 is the supply for the integrated DC-DC converter. Both of these inputs are specified to operate from 3V - 5.5V, so there is no long term reliability concerns with operating the device in the configuration you have described.
However, as the ADM2582E was only characterized with Pin 2 and 8 connected together, when Pin 2 and 8 are run from different supply rails it's possible that some parameters may exceed the maximum and minimum specified characteristics listed in the ADM2587E datasheet.