Power Supplies; Introduction; Independent A/D Converter Supply And Reference Voltage; Independent Usb Transceivers Supply - ST STM32F74 Series Getting Started

AN4661
1

Power supplies

1.1

Introduction

The device requires a 1.8 to 3.6 V operating voltage supply (V
down to 1.7 V with PDR OFF, as detailed in the product datasheets. The embedded linear
voltage regulator is used to supply the internal 1.2 V digital power.
The real-time clock (RTC), the RTC backup registers, and the backup SRAM (BKP SRAM)
can be powered from the V
1.1.1

Independent A/D converter supply and reference voltage

To improve the conversion accuracy, the ADC has an independent power supply which can
be separately filtered and shielded from noise on the PCB.
•
The ADC voltage supply input is available on a separate V
•
An isolated supply ground connection is provided on pin V
To ensure a better accuracy of low voltage inputs, the user can connect a separate external
reference voltage ADC input on V
When available (depending on package), V
1.1.2

Independent USB transceivers supply

The USB transceivers are supplied from a separated V
V can be connected either to V
DDUSB
3.6V) for USB transceivers (refer to
powered at 1.8V, an independent power supply 3.3V can be connected to V
the V
DDUSB
but it must be the last supply to be provided and the first to disappear. The following
conditions V
•
During power-on phase (V
•
During power-down phase (V
•
V
DDSUB
conditions at power-up / power-down (regulator ON) table and operating conditions at
power-up / power-down (regulator OFF) table of STM32F74xxx/STM32F75xxx
datasheet).
•
In operating mode phase, V
–
–
–
BAT
is connected to a separated power supply, it is independent from V
must be respected:
DDUSB
rising and falling time rate specifications must be respected (refer to operating
If USB (USB OTG_HS/OTG_FS) is used, the associated GPIOs powered by
V are operating between V
DDUSB
The V supply both USB transceiver (USB OTG_HS and USB OTG_FS). If
DDUSB
only one USB transceiver is used in the application, the GPIOs associated to the
other USB transceiver are still supplied by V
If USB (USB OTG_HS/OTG_FS) is not used, the associated GPIOs powered by
V are operating between V
DDUSB
DocID027559 Rev 2
voltage when the main V
. The voltage on V
REF
must be externally tied to V
REF–
or an external independent power supply (3.0 to
DD
Figure 1 and Figure
< V ), V
DD DD_MIN DDUSB
< V ), V
DD DD_MIN DDUSB
could be lower or higher than V
DDUSB
DDUSB_MIN
and V
DD_MIN
Power supplies
), which can be reduced
DD
supply is powered off.
DD
pin.
DDA
.
SSA
ranges from 1.8 V to V
REF
power supply pin.
DDUSB
2). For example, when device is
should be always lower than V
should be always lower than V
DD:
and V .
DDUSB_MAX
.
DDUSB
.
DD_MAX
.
DDA
.
SSA
. When
DDUSB
or V
DD DDA
DD
DD
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