23.4.1 Overview

The device is divided into two power supply areas:

  • VDDIO power supply: includes the Supply Controller, part of the Reset Controller, the slow clock switch, the general-purpose backup registers, the supply monitor and the clock which includes the Real-time Timer and the Real-time Clock.
  • Core power supply: includes part of the Reset Controller, the Brownout Detector, the processor, the SRAM memory, the Flash memory and the peripherals.

The Supply Controller (SUPC) controls the supply voltage of the core power supply. The SUPC intervenes when the VDDIO power supply rises (when the system is starting) or when Backup mode is entered.

The SUPC also integrates the slow clock generator, which is based on a 32.768 kHz crystal oscillator, and a slow RC oscillator. The slow clock defaults to the slow RC oscillator, but the software can enable the 32.768 kHz crystal oscillator and select it as the slow clock source.

The SUPC and the VDDIO power supply have a reset circuitry based on a zero-power power-on reset cell. The zero-power power-on reset allows the SUPC to start correctly as soon as the VDDIO voltage becomes valid.

At startup of the system, once the backup voltage VDDIO is valid and the slow RC oscillator is stabilized, the SUPC starts up the core by sequentially enabling the internal voltage regulator. The SUPC waits until the core voltage VDDCORE is valid, then releases the reset signal of the core vddcore_nreset signal.

Once the system has started, the user should program a supply monitor and/or a brownout detector. If the supply monitor detects a voltage level on VDDIO that is too low, the SUPC asserts the reset signal of the core vddcore_nreset signal until VDDIO is valid. Likewise, if the brownout detector detects a core voltage level VDDCORE that is too low, the SUPC asserts the reset signal vddcore_nreset until VDDCORE is valid.

When Backup mode is entered, the SUPC sequentially asserts the reset signal of the core power supply vddcore_nreset and disables the voltage regulator, in order to supply only the VDDIO power supply. Current consumption is reduced to a few microamps for the backup part retention. Exit from this mode is possible on multiple wakeup sources including an event on WKUP pins, or a clock alarm. To exit this mode, the SUPC operates in the same way as system startup.