Datasheet

DocID027590 Rev 4 23/227
STM32F745xx STM32F746xx Functional overview
44
2.15 Boot modes
At startup, the boot memory space is selected by the BOOT pin and BOOT_ADDx option
bytes, allowing to program any boot memory address from 0x0000 0000 to 0x3FFF FFFF
which includes:
• All Flash address space mapped on ITCM or AXIM interface
• All RAM address space: ITCM, DTCM RAMs and SRAMs mapped on AXIM interface
• The System memory bootloader
The boot loader is located in system memory. It is used to reprogram the Flash memory
through a serial interface.
2.16 Power supply schemes
• 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
DD
= 1.7 to 3.6 Vexternal 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 when the internal reset is OFF (refer to
Section 2.17.2: Internal reset OFF). Refer to Table 3: Voltage regulator configuration mode
versus device operating mode to identify the packages supporting this option.
• V
DDUSB
can be connected either to V
DD
or an external independent power supply (3.0
to 3.6V) for USB transceivers (refer to Figure 4 and Figure 5). 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 V
DDUSB
must be respected:
– During power-on phase (V
DD
< V
DD_MIN
), V
DDUSB
should be always lower than
V
DD
– During power-down phase (V
DD
< V
DD_MIN
), V
DDUSB
should be always lower than
V
DD
–V
DDSUB
rising and falling time rate specifications must be respected (see Table 20
and Table 21)
– In operating mode phase, V
DDUSB
could be lower or higher than V
DD:
- 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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