STM32WB15CC datasheet(34/127 Pages) STMICROELECTRONICS

34 / 127 page

Functional overview

STM32WB15CC

34/127

DS13258 Rev 4

3.10

Clocks and startup

The STM32WB15CC device integrates several clock sources:



LSE: 32.768 kHz external oscillator, for accurate RTC and calibration with other

embedded RC oscillators



LSI1: 32 kHz on-chip low-consumption RC oscillator



LSI2: 32 kHz (untrimmable), on-chip temperature stable RC oscillator, can be used by

the RF subsystem instead of LSE



HSE: high quality 32 MHz external oscillator with trimming, needed by the RF

subsystem



HSI16: 16 MHz high accuracy on-chip RC oscillator



MSI: 100 kHz to 48 MHz multiple speed on-chip low power oscillator, can be trimmed

using the LSE signal

The clock controller (see Figure 7) distributes the clocks coming from the different

oscillators to the core and the peripherals including the RF subsystem. 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: four different clock sources can be used to drive the master

clock SYSCLK:

–

16 MHz high-speed internal RC oscillator (HSI16), trimmable by software, that can

supply a PLL

–

Multispeed internal RC oscillator (MSI), trimmable by software, able to generate

12 frequencies from 100 kHz to 48 MHz. When a 32.768 kHz clock source is

available in the system (LSE), the MSI frequency can be automatically trimmed by

hardware to reach better than ±0.25% accuracy. The MSI can supply a PLL.

–

System PLL that can be fed by HSE, HSI16 or MSI, with a maximum frequency of

64 MHz.



Auxiliary clock source: two ultralow-power clock sources that can be used to drive

the real-time clock:

–

32.768 kHz low-speed external crystal (LSE), supporting four drive capability

modes. The LSE can also be configured in bypass mode for an external clock.

–

32 kHz low-speed internal RC (LSI1), also used to drive the independent

watchdog. The LSI1 clock accuracy is ±5%.

–

32 kHz low-speed internal RC (LSI2), with ±200 ppm / °C stability over

temperature.



Peripheral clock sources: Several peripherals (RNG, USARTs, I2C, LPTimers, ADC)

have their own independent clock whatever the system clock. A PLL having three

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