Power Supplies; Introduction; Independent A/D Converter Supply And Reference Voltage; Battery Backup - ST STM32F4 Series Getting Started

AN4488
2

Power supplies

2.1

Introduction

The operating voltage supply (V
1.7 V with some restrictions, as detailed in the product datasheets. An embedded regulator
is used to supply the internal 1.2 V digital power.
The real-time clock (RTC) and backup registers can be powered from the V
when the main V
2.1.1

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
In all cases, the VSSA pin should be externally connected to same supply ground than
VSS
On packages with 100-pins and above
To ensure a better accuracy on low-voltage inputs, the user can connect a separate external
reference voltage ADC input on V
to V with a minimum of 1.7 V.
DDA
When available (depending on package), V
On packages with less than 100-pins
The V
REF+
voltage supply (V
2.1.2

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
supply is powered off.
DD
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
DocID026304 Rev 3
) range is 1.8 V to 3.6 V, which can be reduced down to
DD
. The voltage on V
REF+
must be externally tied to V
REF–
).
SSA
DD
BAT
Power supplies
BAT
pin
DDA
pin
SSA
may range from (V
REF+
SSA
is turned off, the V
BAT
supply is controlled by the power
voltage
- 1.2 V)
DDA
.
pin can be
BAT
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