ADUCM4050 ADC power supply

Hi EZ,

I am currently doing a schematic using the ADUCM4050, and his internal ADC, and I would like to know few stuff : 

• Is that possible to have Vbat_ADC set to a different value than the other Vbat of the microcontroller ? 
• Is that mandatory to have Vbat_ADC = Vref_ADC ? 

I am asking this cause I would like to powered up the ADUCM4050 with 2.5V, and having a Vref for the ADUCM40050 ADC's set to 3.3V (cause we would like to measure voltage up to 3V approximatively).

So is that possible to set : 

Vref_ADC = 3.3V   //   Vbat_ADC=3.3V //   other Vbat=2.5V  

                                             OR

Vref_ADC = 3.3V   //   Vbat_ADC=2.5V //   other Vbat=2.5V  

Thanks for your help,

Florent