ST STM32F20 Series User Manual

AN3320 Power supplies
Doc ID 18267 Rev 2 7/29
1.1.1 Independent A/D converter supply and reference voltage
To improve conversion accuracy, the ADC has an independent power supply that can be
filtered separately, and shielded from noise on the PCB.
● the ADC voltage supply input is available on a separate V
DDA
pin
● an isolated supply ground connection is provided on the V
SSA
pin
When available (depending on package), V
REF–
must be tied to V
SSA
.
On 100-pin package and above and on WLCSP64+2
To ensure a better accuracy on low-voltage inputs, the user can connect a separate external
reference voltage ADC input on V
REF+
. The voltage on V
REF+
may range from 1.8 V to
V
DDA
. On WLCSP64+2, the V
REF-
pin is not available, it is internally connected to the ADC
ground (V
SSA
).
On 64-pin packages
The V
REF+
and V
REF-
pins are not available, they are internally connected to the ADC
voltage supply (V
DDA
) and ground (V
SSA
).
1.1.2 Battery backup
To retain the content of the Backup registers when V
DD
is turned off, the V
BAT
pin can be
connected to an optional standby voltage supplied by a battery or another source.
The V
BAT
pin also powers the RTC unit, allowing the RTC to operate even when the main
digital supply (V
DD
) is turned off. The switch to the V
BAT
supply is controlled by the power
down reset (PDR) circuitry embedded in the Reset block.
If no external battery is used in the application, it is highly recommended to connect V
BAT
externally to V
DD
.
1.1.3 Voltage regulator
The voltage regulator is always enabled after reset. It works in three different modes
depending on the application modes.
● in Run mode, the regulator supplies full power to the 1.2 V domain (core, memories
and digital peripherals)
● in Stop mode, the regulator supplies low power to the 1.2 V domain, preserving the
contents of the registers and SRAM
● in Standby mode, the regulator is powered down. The contents of the registers and
SRAM are lost except for those concerned with the Standby circuitry and the Backup
domain.
Note: Depending on the selected package, there are specific pins that should be connected either
to V
SS
or V
DD
to activate or deactivate the voltage regulator. Refer to section "Voltage
regulator" in STM32F20xxx/21xxx datasheet for details.

ST STM32F20 Series Specifications

General

Brand	ST
Model	STM32F20 Series
Category	Microcontrollers
Language	English