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RM0365
Power control (PWR)
112
V
DD
must always be kept lower than or equal to V
DDA
.
•
VDD18 = 1.65 to 1.95 V (VDD18 domain): power supply for digital core, SRAM and
Flash memory.
VDD18 is internally generated through an internal voltage regulator .
•
V
DDA
, V
SSA
= 2.0 to 3.6 V : external power supply for ADC, DAC, comparators,
operational amplifiers, temperature sensor, PLL, HSI 8 MHz oscillator, LSI 40 kHz
oscillator, and reset block.
V
DDA
must be in the 2.4 to 3.6 V range when the OPAMP and DAC are used.
It is forbidden to have V
DDA
< V
DD
- 0.4 V. An external Schottky diode must be placed
between V
DD
and V
DDA
to guarantee that this condition is met.
•
V
BAT
= 1.65 to 3.6 V: Backup power supply for RTC, LSE oscillator, PC13 to PC15 and
backup registers when V
DD
is not present. When V
DD
supply is present, the internal
power switch switches the backup power to V
DD
. If V
BAT
is not used, it must be
connected to V
DD
.
8.1.1
Independent A/D and D/A converter supply and reference voltage
To improve conversion accuracy, the ADC and the DAC have an independent power supply
which can be separately filtered and shielded from noise on the PCB.
The ADC and DAC voltage supply input is available on a separate VDDA pin. An isolated
supply ground connection is provided on the VSSA pin.
144- and 100-pin package connections (only on STM32F302xB/CD/E)
To ensure a better accuracy on low-voltage inputs and outputs, a separate external
reference voltage can be connected on VREF+. VREF+ is the highest voltage, represented
by the full scale value, for an analog input (ADC) or output (DAC) signal.
64-pin, 49-pin, 48-pin and 32-pin package connections
On these packages, the VREF+ and VREF- pins are not available. They are internally
connected to the ADC voltage supply (V
DDA
) and ground (V
SSA
) respectively.
The V
DDA
supply/reference voltage can be equal to or higher than V
DD
. 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.
When V
DDA
is different from V
DD
, V
DDA
must always be higher or equal to V
DD
. To maintain
a safe potential difference between V
DDA
and V
DD
during power-up/power-down, an
external Schottky diode can be used between V
DD
and V
DDA
. Refer to the datasheet for the
maximum allowed difference.
8.1.2 Battery
backup
domain
To retain the content of the Backup registers and supply the RTC function when V
DD
is
turned off, V
BAT
pin can be connected to an optional standby voltage supplied by a battery
or by another source.
The V
BAT
pin powers the RTC unit, the LSE oscillator and the PC13 to PC15 I/Os, allowing
the RTC to operate even when the main power supply is turned off. The switch to the V
BAT
supply is controlled by the Power Down Reset embedded in the Reset block.