Datasheet
Functional overview STM32F446xC/E
22/202 DocID027107 Rev 6
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, I
2
C, CAN, SPI and USB) communication interface. Refer to
application note AN2606 for details.
3.15 Power supply schemes
• V
DD
= 1.7 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, DAC, Reset
blocks, RCs and PLL. V
DDA
and V
SSA
must be connected to V
DD
and V
SS
, respectively.
Note: V
DD
/V
DDA
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.
• 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.
• V
DDUSB
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 V
DDUSB
. When the V
DDUSB
is connected to a separated power supply,
it is independent from V
DD
or V
DDA
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 (V
DD
< 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, V
DDUSB
could be lower or higher than VDD:
– If USB (USB OTG_HS/OTG_FS) is used, the associated GPIOs powered by
V
DDUSB
are operating between V
DDUSB_MIN
and V
DDUSB_MAX
.The V
DDUSB
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 V
DDUSB
.
– If USB (USB OTG_HS/OTG_FS) is not used, the associated GPIOs powered
by V
DDUSB
are operating between V
DD_MIN
and V
DD_MAX
.
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