Datasheet

Functional overview STM32F401xB STM32F401xC
18/139 DS9716 Rev 11
3.11 Clocks and startup
On reset the 16 MHz internal RC oscillator is selected as the default CPU clock. The
16 MHz internal RC oscillator is factory-trimmed to offer 1% accuracy at 25 °C. The
application can then select as system clock either the RC oscillator or an external 4-26 MHz
clock source. This clock can be monitored for failure. If a failure is detected, the system
automatically switches back to the internal RC oscillator and a software interrupt is
generated (if enabled). This clock source is input to a PLL thus allowing to increase the
frequency up to 84 MHz. Similarly, full interrupt management of the PLL clock entry is
available when necessary (for example if an indirectly used external oscillator fails).
Several prescalers allow the configuration of the two AHB buses, the high-speed APB
(APB2) and the low-speed APB (APB1) domains. The maximum frequency of the two AHB
buses is 84 MHz while the maximum frequency of the high-speed APB domains is 84 MHz.
The maximum allowed frequency of the low-speed APB domain is 42 MHz.
The devices embed a dedicated PLL (PLLI2S) which allows to achieve audio class
performance. In this case, the I
2
S master clock can generate all standard sampling
frequencies from 8 kHz to 192 kHz.
3.12 Boot modes
At startup, boot pins are used to select one out of three boot options:
• Boot from user Flash
• Boot from system memory
• Boot from embedded SRAM
The bootloader is located in system memory. It is used to reprogram the Flash memory by
using either USART1(PA9/10), USART2(PD5/6), USB OTG FS in device mode (PA11/12)
through DFU (device firmware upgrade), I2C1(PB6/7), I2C2(PB10/3), I2C3(PA8/PB4),
SPI1(PA4/5/6/7), SPI2(PB12/13/14/15) or SPI3(PA15, PC10/11/12).
For more detailed information on the bootloader, refer to Application Note: AN2606, STM32
microcontroller system memory boot mode.
3.13 Power supply schemes
• V
DD
= 1.7 to 3.6 V: external power supply for I/Os with the internal supervisor
(POR/PDR) disabled, provided externally through V
DD
pins. Requires the use of an
external power supply supervisor connected to the VDD and PDR_ON pins.
• V
DD
= 1.8 to 3.6 V: external power supply for I/Os and the internal regulator (when
enabled), provided externally through V
DD
pins.
• V
SSA
, V
DDA
= 1.7 to 3.6 V: external analog power supplies for ADC, Reset blocks, RCs
and PLL. V
DDA
and V
SSA
must be connected to V
DD
and V
SS
, respectively, with
decoupling technique.
• V
BAT
= 1.65 to 3.6 V: power supply for RTC, external clock 32 kHz oscillator and
backup registers (through power switch) when V
DD
is not present.
Refer to Figure 18: Power supply scheme for more details.
Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.