The internal 1.8-V Voltage Regulator (VREG) generates VDD18 power from VDDIO. The 1.8-V VREG is enabled by pulling the VREG18EN pin to a low state. When enabled, the 1.8-V VREG provides 1.8 V to digital logic associated with the analog functions of the Analog Subsystem.
When the internal 1.8-V VREG function is enabled, the 1.8 V power no longer has to be provided externally; however, a 1.2-µF (10% tolerance) capacitor is required for each VDD18 pin to stabilize the internally generated voltages. These load capacitors are not required if the internal 1.8-V VREG is disabled, and the 1.8 V is provided from an external supply.
While removing the need for an external power supply, enabling the internal VREG might affect the VDDIO power consumption.