Datasheet

DocID025936 Rev 8 23/143
STM32L052x6 STM32L052x8 Functional overview
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3.4.3 Voltage regulator
The regulator has three operation modes: main (MR), low power (LPR) and power down.
• MR is used in Run mode (nominal regulation)
• LPR is used in the Low-power run, Low-power sleep and Stop modes
• Power down is used in Standby mode. The regulator output is high impedance, the
kernel circuitry is powered down, inducing zero consumption but the contents of the
registers and RAM are lost except for the standby circuitry (wakeup logic, IWDG, RTC,
LSI, LSE crystal 32 KHz oscillator, RCC_CSR).
3.5 Clock management
The clock controller distributes the clocks coming from different oscillators to the core and
the peripherals. It also manages clock gating for low-power modes and ensures clock
robustness. It features:
• Clock prescaler
To get the best trade-off between speed and current consumption, the clock frequency
to the CPU and peripherals can be adjusted by a programmable prescaler.
• Safe clock switching
Clock sources can be changed safely on the fly in Run mode through a configuration
register.
• Clock management
To reduce power consumption, the clock controller can stop the clock to the core,
individual peripherals or memory.
• System clock source
Three different clock sources can be used to drive the master clock SYSCLK:
– 1-25 MHz high-speed external crystal (HSE), that can supply a PLL
– 16 MHz high-speed internal RC oscillator (HSI), trimmable by software, that can
supply a PLLMultispeed internal RC oscillator (MSI), trimmable by software, able
to generate 7 frequencies (65 kHz, 131 kHz, 262 kHz, 524 kHz, 1.05 MHz, 2.1
MHz, 4.2 MHz). When a 32.768 kHz clock source is available in the system (LSE),
the MSI frequency can be trimmed by software down to a ±0.5% accuracy.
• Auxiliary clock source
Two ultra-low-power clock sources that can be used to drive the real-time clock:
– 32.768 kHz low-speed external crystal (LSE)
– 37 kHz low-speed internal RC (LSI), also used to drive the independent watchdog.
The LSI clock can be measured using the high-speed internal RC oscillator for
greater precision.
• RTC clock source
The LSI, LSE or HSE sources can be chosen to clock the RTC, whatever the system
clock.
• USB clock source
A 48 MHz clock trimmed through the USB SOF supplies the USB interface.
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