19.6.1.4 Voltage Scaling Control

The VDDCORE supply will change under these circumstances:
  • When a Sleep mode (Standby, Hibernate, Backup) is entered or exited
  • When a sleepwalking task is requested in Standby mode

To prevent high peak current on the main power supply and to have a smooth transition of VDDCORE, the Voltage Scaling Period field in VREG (VREG.VSPER) can be controlled: VDDCORE is changed by a typical 5 mV of the selected voltage scaling period (2VSPER) * T until the target voltage is reached.

The smooth transition of VDDCORE is enabled/disabled by setting/clearing the Voltage Scaling Enable bit in VREG (VREG.VSEN).

The following waveform shows an example of exiting the Standby Sleep mode.

The STATUS.VCORERDY bit is set to '1' as soon as the VDDCORE voltage has reached the target voltage. During voltage transition, STATUS.VCORERDY will read '0'. The Voltage Ready interrupt (VCORERDY) can be used to detect a 0-to-1 transition of STATUS.VCORERDY, see also “Interrupts”.

When entering the Standby, Hibernate, or Backup Sleep mode, and when no sleepwalking task is requested, the VDDCORE Voltage scaling control is not used. This means that the voltage scale rise rate control (smooth transition) operates only when the device exits from sleep modes, and when the device is already in standby sleep mode and sleep walking is requested.