Datasheet

DocID025409 Rev 8 15/121
STM32F334x4 STM32F334x6 STM32F334x8 Functional overview
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remains in reset mode when the monitored supply voltage is below a specified threshold,
V
POR/PDR, without the need for an external reset circuit.
• The POR monitors only the V
DD
supply voltage. During the startup phase it is required
that V
DDA
must arrive first and be greater than or equal to V
DD
.
• The PDR monitors both the V
DD
and V
DDA
supply voltages, however the V
DDA
power
supply supervisor can be disabled (by programming a dedicated Option bit) to reduce
the power consumption if the application design ensures that V
DDA
is higher than or
equal to V
DD
.
The device features an embedded programmable voltage detector (PVD) that monitors the
V
DD
power supply and compares it to the VPVD threshold. An interrupt can be generated
when V
DD
drops below the V
PVD
threshold and/or when V
DD
is higher than the V
PVD
threshold. The interrupt service routine can then generate a warning message and/or put
the MCU into a safe state. The PVD is enabled by software.
3.4.3 Voltage regulator
The regulator has three operation modes: main (MR), low-power (LPR), and power-down.
• The MR mode is used in the nominal regulation mode (Run)
• The LPR mode is used in Stop mode.
• The power-down mode is used in Standby mode: the regulator output is in high
impedance, and the kernel circuitry is powered down thus inducing zero consumption.
The voltage regulator is always enabled after reset. It is disabled in Standby mode.
3.4.4 Low-power modes
The STM32F334x4/6/8 supports 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
Stop mode achieves the lowest power consumption while retaining the content of
SRAM and registers. All clocks in the 1.8 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 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, COMPx,
I
2
C or USARTx.
• Standby mode
The Standby mode is used to achieve the lowest power consumption. The internal
voltage regulator is switched off so that the entire 1.8 V domain is powered off. The
PLL, the HSI RC and the HSE crystal oscillators are also switched off. After entering
Standby mode, SRAM and register contents are lost except for registers in the Backup
domain and Standby circuitry.
The device exits Standby mode when an external reset (NRST pin), an IWDG reset, a
rising edge on the WKUP pin, or an RTC alarm occurs.
Note: The RTC, the IWDG, and the corresponding clock sources are not stopped by entering Stop
or Standby mode.
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