Datasheet

Functional overview STM32L071xx
22/144 DS10690 Rev 6
internal reference voltage (V
REFINT
) in Stop mode. The device remains in reset mode when
V
DD
is below a specified threshold, V
POR/PDR
or V
BOR
, without the need for any external
reset circuit.
Note: The start-up time at power-on is typically 3.3 ms when BOR is active at power-up, the start-
up time at power-on can be decreased down to 1 ms typically for devices with BOR inactive
at power-up.
The devices feature an embedded programmable voltage detector (PVD) that monitors the
V
DD/VDDA
power supply and compares it to the V
PVD
threshold. This PVD offers 7 different
levels between 1.85 V and 3.05 V, chosen by software, with a step around 200 mV. An
interrupt can be generated when V
DD/VDDA
drops below the V
PVD
threshold and/or when
V
DD/VDDA
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.
• 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:
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