negative ground with ADuM7440

I would like to hook up an ADuM7440 to convert 4 signals from NEGCMOS [Logic ‘1’ = 0V, Logic ‘0’ = -5V] to normal +3.3V LVCMOS [Logic ‘1’ = +3.3V, Logic ‘0’ = 0V] on the other side.

  NEGCMOS side:
   VDD1 -  GND
   GND1 -   -5V

LVCMOS side:

   VDD2 - +3.3V
   GND2 - GND

this is acceptable?  The datasheet seems to imply that only positive rails are acceptable, even though the 1kV of digital isolation should be sufficient. 

  • You can hook up the ADuM7440 this way.  Just make sure that Vix doesn’t exceed 0.5V or fall below -5.5V.  The data sheet says -0.5V for the absolute minimum voltage for Vin, but it assumes a 0V ground.  It’s warning you not to have Vix below their ground - 0.5V.  Basically you have 5VDC across the grounds, which is well within the 148Vrms working voltage for this part.