19.5.3.3.2.2 Regulator Automatic Low-Power Mode

In Standby mode, the PM selects either the main or the low-power voltage regulator to supply the VDDCORE. By default the low-power voltage regulator is used.

If a sleepwalking task is working on either asynchronous clocks (generic clocks) or synchronous clock (APB/AHB clocks), the main voltage regulator is used. This behavior can be changed by writing the Voltage Regulator Standby Mode bits in the Standby Configuration register (STDBYCFG.VREGSMOD). Refer to the following table for details.