hi can

vdda1

be 1.8V? Is there any circuit in pad can prevent voltage lower than 3.3v? @Mitch Bailey

I have heard that vdda1 and/or vdda2 can be 1.8V but you may need to physically modify the board. @Tim Edwards can probably give you a definitive answer.

There are no restrictions on

vdda1

other than that the voltage clamp is rated between 1.8V and 5.5V, and I cannot say if it operates correctly outside of those ranges. The

vdda1/2

domains are otherwise unconnected, and the header pins for both have to be physically jumpered to apply any voltage at all, so you don't need to make any changes to the board.