AT32F421
Series Reference Manual
2022.11.11
Page 41
Rev 2.02
Figure 3-3 PVM threshold and output
PVMOF
VDD
100 mV
hysteresis
V
DET_P
+ V
HYS_P
V
DET_P
T
PLH
T
PHL
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, LEXT oscillator and all PAD circuits. The VDDA domain contains an ADC (AD converter),
temperature sensor 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. The 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 a 1.2 V power (for CPU core, memories and
embedded peripherals) as it is in normal power consumption mode.
1)
If the WFI is executed to enter Sleep mode, any peripheral interrupt can wake up the device from
Sleep mode.