Datasheet

Functional overview STM32F401xD STM32F401xE
26/135 DocID025644 Rev 3
The RTC and backup registers are supplied through a switch that is powered either from the
V
DD
supply when present or from the V
BAT
pin.
3.17 Low-power modes
The devices support three low-power modes to achieve the best compromise between low
power consumption, short startup time and available wakeup sources:
• Sleep mode
In Sleep mode, only the CPU is stopped. All peripherals continue to operate and can
wake up the CPU when an interrupt/event occurs.
• Stop mode
The Stop mode achieves the lowest power consumption while retaining the contents of
SRAM and registers. All clocks in the 1.2 V domain are stopped, the PLL, the HSI RC
and the HSE crystal oscillators are disabled. The voltage regulator can also be put
either in normal or in low-power mode.
The device can be woken up from the Stop mode by any of the EXTI line (the EXTI line
source can be one of the 16 external lines, the PVD output, the RTC alarm/ wakeup/
tamper/ time stamp events).
• Standby mode
The Standby mode is used to achieve the lowest power consumption. The internal
voltage regulator is switched off so that the entire 1.2 V domain is powered off. The
PLL, the HSI RC and the HSE crystal oscillators are also switched off. After entering
Standby mode, the SRAM and register contents are lost except for registers in the
backup domain when selected.
The device exits the Standby mode when an external reset (NRST pin), an IWDG reset,
a rising edge on the WKUP pin, or an RTC alarm/ wakeup/ tamper/time stamp event
occurs.
Standby mode is not supported when the embedded voltage regulator is bypassed and
the 1.2 V domain is controlled by an external power.
3.18 V
BAT
operation
The VBAT pin allows to power the device V
BAT
domain from an external battery, an external
super-capacitor, or from V
DD
when no external battery and an external super-capacitor are
present.
V
BAT
operation is activated when V
DD
is not present.
The VBAT pin supplies the RTC and the backup registers.
Note: When the microcontroller is supplied from VBAT, external interrupts and RTC alarm/events
do not exit it from V
BAT
operation. When PDR_ON pin is not connected to V
DD
(internal
Reset OFF), the V
BAT
functionality is no more available and VBAT pin should be connected
to V
DD
.
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