I use the AD7918 to measure internal voltages of my electronic, namely 15V, 5V and 3.3V itself. Due to the Power Supply topology, the 15VDC are generated ny a separate switch mode regulator than the 5VDC and 3.3V (derived of 5V). Thus I cannot exclude conditions with the 15VDC being applied to the input channel of the ADC w/o having the 3.3V already powering the ADC itself. For the ADC failed with a significant rate in the last two weeks I took a deeper look into the Datasheet and by this I found (somewhere in the text)...
"If CS, DIN, or SCLK are applied before AVDD, there is no risk of latch-up as there would be on the analog inputs if a signal greater than 0.3 V was applied prior to AVDD. "
Does this indicates potential problems with signal being applied to the analog input channel w/o AVDD (3.3VDC) being applied (which may happen in my circuit)? Curiously we built more than thousand units up to now w/o facing any issue and last weeks 4 ADC failed with defect measurement of the 15VDC, that initiated my search for a root cause. Can the analog input be protected by higher ohmic voltage divider scaling to minimize any input current into the analog channel?
Thanks a lot,Carlhermann