STM32F446RC datasheet(22/201 Pages) STMICROELECTRONICS

22 / 201 page

Functional overview

STM32F446xC/E

22/201

DocID027107 Rev 5

3.14

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

through a serial (UART, I2C, CAN, SPI and USB) communication interface. Refer to

application note AN2606 for details.

3.15

Power supply schemes

•

VDD = 1.7 to 3.6 V: external power supply for I/Os and the internal regulator (when

enabled), provided externally through VDD pins.

•

VSSA, VDDA = 1.7 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.

Note:

VDD/VDDA minimum value of 1.7 V is obtained with the use of an external power supply

supervisor (refer to Section 3.16.2: Internal reset OFF). Refer to Table 3: Voltage regulator

configuration mode versus device operating mode to identify the packages supporting this

option.

•

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.

•

VDDUSB can be connected either to VDD or an external independent power supply (3.0

to 3.6V) for USB transceivers.

For example, when device is powered at 1.8V, an independent power supply 3.3V can

be connected to VDDUSB. When the VDDUSB is connected to a separated power supply,

it is independent from VDD or VDDA but it must be the last supply to be provided and the

first to disappear. The following conditions VDDUSB must be respected:

–

During power-on phase (VDD < VDD_MIN), VDDUSB should be always lower than

VDD

–

During power-down phase (VDD < VDD_MIN), VDDUSB should be always lower

than VDD

–

VDDUSB rising and falling time rate specifications must be respected.

–

In operating mode phase, VDDUSB could be lower or higher than VDD:

– If USB (USB OTG_HS/OTG_FS) is used, the associated GPIOs powered by

VDDUSB are operating between VDDUSB_MIN and VDDUSB_MAX.The VDDUSB

supply both USB transceiver (USB OTG_HS and USB OTG_FS).

– If only one USB transceiver is used in the application, the GPIOs associated to

the other USB transceiver are still supplied by VDDUSB.

– If USB (USB OTG_HS/OTG_FS) is not used, the associated GPIOs powered

by VDDUSB are operating between VDD_MIN and VDD_MAX.

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