AN3320 datasheet(7/29 Pages) STMICROELECTRONICS

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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 VDDA pin

●

an isolated supply ground connection is provided on the VSSA pin

When available (depending on package), VREF– must be tied to VSSA.

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 VREF+. The voltage on VREF+ may range from 1.8 V to

VDDA. On WLCSP64+2, the VREF- pin is not available, it is internally connected to the ADC

ground (VSSA).

On 64-pin packages

The VREF+ and VREF- pins are not available, they are internally connected to the ADC

voltage supply (VDDA) and ground (VSSA).

1.1.2

Battery backup

To retain the content of the Backup registers when VDD is turned off, the VBAT pin can be

connected to an optional standby voltage supplied by a battery or another source.

The VBAT pin also powers the RTC unit, allowing the RTC to operate even when the main

digital supply (VDD) is turned off. The switch to the VBAT 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 VBAT

externally to VDD.

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 VSS or VDD to activate or deactivate the voltage regulator. Refer to section "Voltage

regulator" in STM32F20xxx/21xxx datasheet for details.

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