I am using the AD7794 with separate analog and digital power supplies. I have noticed that if I disconnect the digital power supply, I get some voltage on the otherwise disconnected digital supply pin (about 0.5 V less than the analog supply voltage). I assume that in this (irregular) configuration, some protection diodes start conducting somewhere in within AD7794. This is creates some problems, because now the digital part of my systems gets some power via this connection and it is not working as expected.
My questions are:
Is this behaviour normal (is there really a current path from the analog to digital power supply and viceversa)?
Will AD7794 be destroyed if either analog or digital supply is missing (due to power supply failure or different switch on times)?
Should I place a diode before the digital supply pin on AD7794 to prevent the DVDD pin to act as the power source for the rest of the digital circuitry?
Is there some reference schematic that shows exactly how the AVDD and DVDD are related within the AD7794?