AT32F425
Series Reference Manual
2022.03.30
Page 45
Ver 2.01
3.5 Power domain
1.2 V domain
1.2 V core domain includes a CPU core, SRAM, embedded digital peripherals and Phase Locked Loop
(PLL). Such power domain is supplied by LDO (voltage regulator).
VDD/VDDA domain
VDD/VDDA domain includes VDD domain and VDDA domain. The VDD domain contains I/O circuit,
power-saving mode wakeup circuit, watchdog timer (WDT), power-on reset/low voltage reset (POR/LVR),
LDO, ERTC circuit, LEXT oscillator and and all PAD circuits. The VDDA domain contains a ADC (AD
converters), and so on.
Typically, to ensure a better accuracy of ADC at a low voltage, the digital circuit is supplied by VDD while
the analog circuit is powered by VDDA. he external reference voltage VREF+ and VREF- are connected
to the VDDA pin and VSSA pin, respectively.
3.6 Power saving modes
When the CPU does not need to be kept running, there are three types of low-power modes available
(Sleep mode, Deepsleep mode and Standby mode) to save power. Users can select the mode that gives
the best compromise according to the low-power consumption, short startup time, and available wakeup
sources. In addition, the power consumption in Run mode can be reduced by slowing down the system
clocks or gating the clocks to the APB and AHB peripherals when they are not used.
Sleep mode
The Sleep mode is entered by executing WFI or WFE instruction. There are two options to select the
Sleep mode entry mechanism through the SLEEPONEXIT bit in the Cortex ® -M4 system control register.
SLEEP-NOW mode:
When SLEEPDEEP=0 and SLEEPONEXIT=0, the MCU enters Sleep mode as soon as WFI or WFE
instruction is executed.
When SLEEPDEEP=0 and SLEEPONEXIT=1, the MCU enters Sleep mode as soon as the system exits
the lowest-priority interrupt service routine by executing the WFI instruction.
In Sleep mode, all clocks and LDO work normally except CPU clocks (stopped), and all I/O pins keep
the same state as in Run mode. The LDO provides an 1.2 V power (for CPU core, memory and
embedded peripherals) as it is in normal power consumption mode. The LDO output voltage is
configurable by the PWC_LDOOV register.
1)
If the WFI is executed to enter Sleep mode, any peripheral interrupt can wake up the device from
Sleep mode.
2)
If the WFE is executed to enter Sleep mode, the MCU exits Sleep mode as soon as an event occurs.
The wakeup event can be generated by the following:
Enabling a peripheral interrupt (it is not enabled in the NVIC) and enabling the SEVONPEND bit.
When the MCU resumes, the peripheral interrupt pending bit and NVIC channel pending bit must
be cleared.
Configuring an internal EXINT line as an event mode to generate a wakeup event.
The wakeup time required by a WFE instruction is the shortest, since no time is wasted on
interrupt entry/exit.
Deepsleep Mode
Deepsleep mode is entered by setting the SLEEPDEEP bit in the Cortex
™
-M4 system control register
and clearing the LPSEL bit in the power control register before WFI or WFE instructions.
The LDO status is selected by setting the VRSEL bit in the power control register (PWC_CTRL). When
VRSEL=0, the LDO works in normal mode. When VRSEL=1, the LDO is set in low-power consumption
mode.
In Deepsleep mode, all clocks in 1.2 V domain are stopped, and both HICK and HEXT oscillators are
disabled. The LDO supplies power to the 1.2 V domain in normal mode or low-power mode. All I/O pins
keep the same state as in Run mode. SRAM and register contents are preserved.
1)
When the Sleep mode is entered by executing a WFI instruction, the interrupt generated on any