Independent I/O Supply Rail; Independent Usb Transceiver Supply; Battery Backup Domain - ST STM32U5 Getting Started

ADC and DAC reference voltage
To ensure a better accuracy on low-voltage inputs and outputs, the user can connect to VREF+ pin, a separate
reference voltage lower than V
V is the highest voltage, represented by the full-scale value, for an analog input (ADC) or output (DAC)
REF+
signal. V
REF+
voltage: 1.5, 1.8, 2.048 or 2.5 V. The VREFBUF can also provide the voltage to external components through the
VREF+ pin.
For further information, refer to the device datasheet and section Voltage reference buffer (VREFBUF) of
document [1].
2.1.2

Independent I/O supply rail

Some I/Os from port G (PG[15:2]) are supplied from a separate supply rail. The power supply for this rail can
range from 1.08 V to 3.6 V, and is provided externally through the VDDIO2 pin. The V
completely independent from V
The VDDIO2 pin is available only for some packages (refer to the pinout details in the datasheet for the I/O list).
After reset, the I/Os supplied by V
The isolation must be removed before using any I/O from PG[15:2], by setting the IO2SV bit in PWR_SVMR, once
the V supply is present.
DDIO2
The V supply is monitored by the V
DDIO2
reference voltage (3/4 V
For more details, refer to the device datasheet and section Peripheral voltage monitoring (PVM) of document [1].
2.1.3

Independent USB transceiver supply

The USB transceivers are supplied from a separate V
and is completely independent from V
After reset, the USB features supplied by V
available. The isolation must be removed before using the USB OTG peripheral, by setting the USV bit in the
PWR_SVMR register, once the V
The V supply is monitored by the USB voltage monitoring (UVM) and compared with the internal reference
DDUSB
voltage (V
REFINT
monitoring (PVM) of document [1].
For STM32U59x/5Ax/5Fx/5Gx devices only, the USB high-speed transceiver can be supplied from an optional
power supply V
2.1.4

Battery backup domain

To retain the content of the backup registers and supply the RTC when V
connected to an optional backup voltage, supplied by a battery or by another source.
The VBAT pin powers RTC, TAMP, LSE oscillator, and PC13 to PC15 I/Os. That allows the RTC to operate even
when the main power supply is turned off.
The backup SRAM is optionally powered through the VBAT pin, when the BREN bit is set in PWR_BDCR1.
The switch to the V
Caution: • During t
between V
• During the startup phase, if V
t
RSTTEMPO
internal diode connected between the VDD pin and the power switch (VBAT). If the power supply/battery
connected to the VBAT pin cannot support this current injection, it is strongly recommended to connect an
external low-drop diode between this power supply and the VBAT pin.
If no external battery is used in the application, it is recommended to connect the VBAT pin externally to V
a 100 nF external ceramic decoupling capacitor.
AN5373 - Rev 6
.
DDA
can be provided either by an external reference or by the VREFBUF that can output a configurable
or V
DD DDA
are logically and electrically isolated and are therefore not available.
DDIO2
DDIO2
, around 0.9 V).
REFINT
or V
DD
supply is present.
DDUSB
, around 1.2 V). For more details, refer to the device datasheet and section Peripheral voltage
. V range is from 1.0 V to 1.26 V and must be connected to V
DD11USB DD11USB
supply is controlled by the power-down reset embedded in the reset block.
BAT
(at V startup) or after a PDR (power-down reset) detection, the power switch
RSTTEMPO DD
and V remains connected to the VBAT pin.
BAT DD
is established in less than t
DD
value), and V > V + 0.6 V, a current may be injected into the VBAT pin through an
DD BAT
.
voltage monitoring (IO2VM) and compared with the internal
power supply. V
DDUSB
.
DDA
are logically and electrically isolated, and are therefore not
DDUSB
RSTTEMPO
Power supplies
voltage level is
DDIO2
range is from 3.0 V to 3.6 V
DDUSB
.
DD11
is turned off, the VBAT pin can be
DD
(refer to the datasheet for
AN5373
with
DD
page 11/47