VCCA-> Connect these pins to a 3.0- or 3.3-V power supplies even if the PLL and ADC are not used.
VCCA_ADC -> Tie the VCCA_ADC pin to any 2.5 V power domain if you are not using ADC.and do not tie the VCCA_ADC pin to GND.
ADC_VREF->If you are not using the external reference, this pin is a no connect (NC).
Thanks for your reply.
I don't have 2.5V in my board & not using ADC , still i need to give VCCA_ADC pin 2.5V ?
Why can't i connect VCCA_ADC to 3.3V?
From my board perspective, 2.5V voltage regulator will add cost to the board unnecessarily. Please help me to understand.
You can check the Power Supplies Recommended Operating Conditions from data sheet. VCCA_ADC maximum Operating voltage can be 2.625.
3.3V is under absolute maximum rating, Device should not operate under in absolute maximum rating, which may cause permanent damage to the device.