Solid decoupling on both the digital and analog supplies is required (best with two capacitors per supply, one 1 µF and one 100 nF [see Section 10.1.1]).

The LDO module is in its own power domain on chip (separate from DVCC). To use the Port U pins (PU.0 and PU.1) this domain must be powered. If use of the Port U pins is needed and no voltage is supplied to LDOI, then a 3.3-V supply to LDOO is needed. LDOO can act as an input only when the 3.3-V LDO is not enabled. When the 3.3-V LDO is not needed in applications, keep LDOI tied low to make sure that the LDO module does not draw excessive current when disabled.