I'd like to use an external +3.3V as the VREF for an AD7699; it's the power supply for the sensors which will operate ratiometrically against it so using it as the reference at least knocks out one source of error. I'm trying to get a sense of my ADC error in this case.
1) It seems like in this application I want to overdrive the REF pin directly rather than use REFIN and the buffer; the buffer doesn't sound like it gains me much here. Is that accurate?
2) All of the accuracy specs in the datasheet are provided for "VREF = 4.096 to VDD". If I keep a 5V VDD, but use an external REF of only +3.3V, how much degradation of these specs can I expect? Offhand I'd expect offset and linearity worse by less than 2:1 and gain error no change, but that's some very crude guesswork
Thanks,
Rob
