Power supplies
AN2586 - Application note
1.1 Introduction
The device requires a 2.0 V to 3.6 V operating voltage supply (V
DD
). An embedded regulator
is used to supply the internal 1.8 V digital power.
The real-time clock (RTC) and backup registers can be powered from the V
BAT
voltage when
the main V
DD
supply is powered off.
Figure 1.
Power supply overview
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 packages
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 2.0 V to
V
DDA
.
A/D converter
V
DDA
V
DD
V
SSA
V
REF+
V
BAT
V
SS
I/O Ring
BKP registers
Temp. sensor
Reset block
Standby circuitry
PLL
(Wakeup logic,
IWDG)
RTC
Voltage regulator
Core
memories'
digital
peripherals
Low voltage detector
V
REF-
V
DDA
domain
V
DD
domain
1.8 V domain
Backup domain
LSE crystal 32K osc
RCC BDCR register
ai14602b
