
Power control (PWR)
RM0351
152/1830
DocID024597 Rev 5
The V
DDA
supply voltage can be different from V
DD
. The presence of V
DDA
must be checked
before enabling any of the analog peripherals supplied by V
DDA
(A/D converter, D/A
converter, comparators, operational amplifiers, voltage reference buffer).
The V
DDA
supply can be monitored by the Peripheral Voltage Monitoring, and compared
with two thresholds (1.65 V for PVM3 or 2.2 V for PVM4), refer to
When a single supply is used, V
DDA
can be externally connected to V
DD
through the
external filtering circuit in order to ensure a noise-free V
DDA
reference voltage.
ADC and DAC reference voltage
To ensure a better accuracy on low-voltage inputs and outputs, the user can connect to
V
REF+
a separate reference voltage lower than V
DDA
. V
REF+
is the highest voltage,
represented by the full scale value, for an analog input (ADC) or output (DAC) signal.
V
REF+
can be provided either by an external reference of by an internal buffered voltage
reference (VREFBUF).
The internal voltage reference is enabled by setting the ENVR bit in the
and status register (VREFBUF_CSR)
. The voltage reference is set to 2.5 V when the VRS
bit is set and to 2.048 V when the VRS bit is cleared. The internal voltage reference can also
provide the voltage to external components through V
REF+
pin. Refer to the device
datasheet and to
Section 21: Voltage reference buffer (VREFBUF)
for further information.
5.1.2
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
V
DDIO2
pin. The V
DDIO2
voltage level is completely independent from V
DD
or V
DDA
. The
V
DDIO2
pin is available only for some packages. Refer to the pinout diagrams or tables in the
related device datasheet(s) for I/O list(s).
After reset, the I/Os supplied by V
DDIO2
are logically and electrically isolated and therefore
are not available. The isolation must be removed before using any I/O from PG[15:2], by
setting the IOSV bit in the PWR_CR2 register, once the V
DDIO2
supply is present.
The V
DDIO2
supply is monitored by the Peripheral Voltage Monitoring (PVM2) and compared
with the internal reference voltage (3/4 V
REFINT
, around 0.9V), refer to
Peripheral Voltage Monitoring (PVM)
for more details.
5.1.3
Independent USB transceivers supply
The USB transceivers are supplied from a separate V
DDUSB
power supply pin. V
DDUSB
range is from 3.0 V to 3.6 V and is completely independent from V
DD
or V
DDA
.
After reset, the USB features supplied by V
DDUSB
are logically and electrically isolated and
therefore are not available. The isolation must be removed before using the USB OTG
peripheral, by setting the USV bit in the PWR_CR2 register, once the V
DDUSB
supply is
present.
The V
DDUSB
supply is monitored by the Peripheral Voltage Monitoring (PVM1) and
compared with the internal reference voltage (V
REFINT
, around 1.2 V), refer to
Peripheral Voltage Monitoring (PVM)
for more details.