STM32F405xx datasheet(23/180 Pages) STMICROELECTRONICS

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STM32F405xx, STM32F407xx

Description

Doc ID 022152 Rev 3

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clock entry is available when necessary (for example if an indirectly used external oscillator

fails).

Several prescalers allow the configuration of the three AHB buses, the high-speed APB

(APB2) and the low-speed APB (APB1) domains. The maximum frequency of the three AHB

buses is 168 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 I2S master clock can generate all standard sampling

frequencies from 8 kHz to 192 kHz.

2.2.13

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 boot loader is located in system memory. It is used to reprogram the Flash memory by

using USART1 (PA9/PA10), USART3 (PC10/PC11 or PB10/PB11), CAN2 (PB5/PB13), USB

OTG FS in Device mode (PA11/PA12) through DFU (device firmware upgrade).

2.2.14

Power supply schemes

●

VDD = 1.8 to 3.6 V: external power supply for I/Os and the internal regulator (when

enabled), provided externally through VDD pins.

●

VSSA, VDDA = 1.8 to 3.6 V: external analog power supplies for ADC, DAC, Reset blocks,

RCs and PLL. VDDA and VSSA must be connected to VDD and VSS, respectively.

●

VBAT = 1.65 to 3.6 V: power supply for RTC, external clock 32 kHz oscillator and backup

registers (through power switch) when VDD is not present.

Refer to Figure 19: Power supply scheme for more details.

Note:

VDD/VDDA minimum value of 1.7 V is obtained when the device operates in the 0 to 70 °C

temperature range and an inverted reset signal is applied to PDR_ON.

2.2.15

Power supply supervisor

The power supply supervisor is enabled by holding PDR_ON high.

The device has an integrated power-on reset (POR) / power-down reset (PDR) circuitry

coupled with a Brownout reset (BOR) circuitry. At power-on, BOR is always active, and

ensures proper operation starting from 1.8 V. After the 1.8 V BOR threshold level is reached,

the option byte loading process starts, either to confirm or modify default thresholds, or to

disable BOR permanently. Three BOR thresholds are available through option bytes.

The device remains in reset mode when VDD is below a specified threshold, VPOR/PDR or

VBOR, without the need for an external reset circuit.

The device also features an embedded programmable voltage detector (PVD) that monitors

the VDD/VDDA power supply and compares it to the VPVD threshold. An interrupt can be

generated when VDD/VDDA drops below the VPVD threshold and/or when VDD/VDDA is higher

than the VPVD 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.

STM32F405xx Datasheet(PDF) 23 Page - STMicroelectronics

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