15.4.1 Overview

The Supply Controller (SUPC) is powered by VDDBU and clocked by MD_SCLK (slow clock).

MD_SLCK is always driven by the slow RC oscillator for safety/security reasons.

At power-up, as soon as the VDDBU voltage passes over the VDD3V3 POR threshold voltage, the SUPC sequentially starts the VDDCORE voltage regulator and deactivates the reset of the VDDCORE domain.

The system can be put in Backup mode (Low-power mode) by configuring the SUPC; exit from Backup mode can be triggered by different programmable sources (RTC, RTT, WKUPx pins, Supply Monitor).

When entering or exiting Backup mode, the SUPC controls the VDDCORE voltage regulator and the reset of the VDDCORE domain.

At power-up, TD_SLCK is driven by the slow RC oscillator. Once configured on the 32.768 kHz crystal oscillator, TD_SLCK is driven by this 32.768 kHz crystal oscillator as long as VDDBU voltage is active.

A slow crystal oscillator monitoring circuitry is active in all system modes including Backup mode, and can be configured to automatically switch the TD_SLCK clock source from the slow crystal oscillator to the slow RC oscillator.

The Supply Monitoring section of the SUPC includes a programmable supply monitor on VDD3V3. The output can either generate a software interrupt or a reset of the VDDCORE domain.

The SUPC features a tamper detection circuit on the WKUP[14:0] signals. This detection is active in all power modes. When only VBAT is supplied, 3 tamper detection pins are available (WKUP[2:0]. Upon a tamper detection event, the SUPC can be configured to automatically clear the General-Purpose Backup Registers (GPBR) and the tamper event is routed to the RTC for timestamping purposes.

The SUPC can be configured to control an external power supply, for example an external voltage regulator, by driving the SHDN pin.

To perform a shutdown of the external voltage regulator, the software asserts the SHDN pin by writing SHDW=1 in the Control register (SUPC_CR). The shutdown is active only two MD_SLCK cycles after the write of SUPC_CR. This register is password-protected and so the value written must contain the correct key for the command to be taken into account. As a result, the SHDN pin is driven low and the system is powered down (VDDCORE voltage equals 0).