Hi Brian,
A possible power-up sequence would be as follows: AVDD, VDD, VREF, VDRIVE in any sequence and then apply Vin+ and Vin-, Digital inputs and outputs. If you'll look at the abs max rating of the datasheet, Vin+ and Vin- must be in the range of -0.3V to VREF + 0.3V therefore, VREF must be powered-up first before applying Vin+ and Vin-. This is also the same for VDRIVE and the digital inputs and outputs.
Also please refer to the INITIAL POWER-UP section of the datasheet for intial power-up settings of the ADC.
Let me know if this answers your question.
Regards,
May
