Have a look at the attached image from AN61290. It shows the direction of the Regulator input & outputs. Vdda & Vddd are the inputs to the internal analog & digital regulators respectively and their outputs are Vcca & Vccd.
So we need to provide external voltage source to Vdda/Vddd pins and only external capacitors for Vcca/Vccd pins. But it is not recommended to use this voltage for driving some other circuits in the board.