7.3.1 Starting of Internal Regulator
After power-up of the VDDREG, VDDIO and AVDD supplies (VDDx > POR voltage), the device is set to its initial state and kept in Reset, until the band-gap and internal regulator power has stabilized throughout the device.
The internal regulator provides the internal VDDCORE_SW once the external voltage VDDIO/AVDD and the internal VDDCORE_xx domains reach a stable value, the internal System Reset is released.