AN4661 datasheet(6/33 Pages) STMICROELECTRONICS

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Power supplies

AN4661

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DocID027559 Rev 1

Power supplies

1.1

Introduction

The device requires a 1.8 to 3.6 V operating voltage supply (VDD), which can be reduced

down to 1.7 V with PDR OFF, as detailed in the product datasheets. The embedded linear

voltage regulator is used to supply the internal 1.2 V digital power.

The real-time clock (RTC), the RTC backup registers, and the backup SRAM (BKP SRAM)

can be powered from the VBAT voltage when the main VDD supply is powered off.

1.1.1

Independent A/D converter supply and reference voltage

To improve the conversion accuracy, the ADC has an independent power supply which can

be separately filtered 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 pin VSSA.

To ensure a better accuracy of low voltage inputs, the user can connect a separate external

reference voltage ADC input on VREF. The voltage on VREF ranges from 1.8 V to VDDA.

1.1.2

Independent USB transceivers supply

The USB transceivers are supplied from a separated VDDUSB power supply pin. The

VDDUSB range is from 3.0 V to 3.6 V and is completely independent from VDD or VDDA. It

can be connected either to VDD or an external independent power supply (3.0 to 3.6V) for

USB transceivers. For example, when device is powered at 1.8V, an independent power

supply 3.3V can be connected to VDDUSB.

When the VDDUSB is connected to a separated power supply, it is independent from VDD

or VDDA but it must be the last supply to be provided and the first to disappear.

Note:

The VDDUSB supply both USB transceiver (USS OTG HS and USB OTG FS). If only one

USB transceiver is used in the application, the GPIOs associated to the other USB

transceiver are still supplied at by VDDUSB.

1.1.3

Battery backup domain

Backup domain description

To retain the content of the RTC backup registers, backup SRAM, and supply the RTC when

VDD is turned off, VBAT pin can be connected to an optional standby voltage supplied by a

battery or by another source.

To allow the RTC to operate even when the main digital supply (VDD) is turned off, the

VBAT pin powers the following blocks:

•

The RTC.

•

The LSE oscillator.

•

The backup SRAM when the low-power backup regulator is enabled.

•

PC13 to PC15 I/Os, plus PI8 I/O (when available).

The switch to the VBAT supply is controlled by the power-down reset embedded in the reset

block.

AN4661 Datasheet(PDF) 6 Page - STMicroelectronics

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