Independent A/D Converter Supply And Reference Voltage; Battery Backup; Voltage Regulator - ST STM32F20 Series Application Note

AN3320
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
●
an isolated supply ground connection is provided on the V
When available (depending on package), V
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
V . On WLCSP64+2, the V
DDA
ground (V
On 64-pin packages
The V
REF+
voltage supply (V
1.1.2

Battery backup

To retain the content of the Backup registers when V
connected to an optional standby voltage supplied by a battery or another source.
The V
BAT
digital supply (V
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
externally to V
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 or V
SS
regulator" in STM32F20xxx/21xxx datasheet for details.
REF-
).
SSA
and V pins are not available, they are internally connected to the ADC
REF-
) and ground (V
DDA
pin also powers the RTC unit, allowing the RTC to operate even when the main
) is turned off. The switch to the V
DD
.
DD
to activate or deactivate the voltage regulator. Refer to section "Voltage
DD
Doc ID 18267 Rev 2
must be tied to V
REF–
. The voltage on V
REF+
pin is not available, it is internally connected to the ADC
).
SSA
DD
BAT
Power supplies
pin
DDA
pin
SSA
.
SSA
may range from 1.8 V to
REF+
is turned off, the V
BAT
supply is controlled by the power
pin can be
BAT
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