Power control (PWR) UM0306
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3.1.2 Battery backup
To retain the content of the Backup registers when V
DD
is turned off, V
BAT
pin can be
connected to an optional standby voltage supplied by a battery or by another source.
The V
BAT
pin also powers the RTC unit, allowing the RTC to operate even when the main
digital supply (V
DD
) is turned off. The switch to the V
BAT
supply is controlled by the Power
Down Reset embedded in the Reset block.
If no external battery is used in the application, V
BAT
must be connected externally to V
DD
.
Warning: During the t
RSTTEMPO
temporization at V
DD
startup, the power
switch between V
BAT
and V
DD
remains connected to V
BAT
. As
V
DD
rises fast and may become established during this time,
a current may be injected into V
BAT
through a diode
connected between V
DD
and V
BAT
when V
BAT
is lower than
V
DD
−0.6V
.
Refer to the datasheet for the value of t
RSTTEMPO.
3.1.3 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 1.8 V domain (core, memories
and digital peripherals).
● In STOP mode the regulator supplies low-power to the 1.8 V domain, preserving
contents of registers and SRAM
● In STANDBY Mode, the regulator is powered off. The contents of the registers and
SRAM are lost except for the STANDBY circuitry and the Backup Domain.
3.2 Power supply supervisor
3.2.1 Power On Reset (POR)/Power Down Reset (PDR)
The device has an integrated POR/PDR circuitry that allows proper operation starting
from/down to 2 V.
The device remains in Reset mode when V
DD
is below a specified threshold, V
POR/PDR
,
without the need for an external reset circuit. For more details concerning the Power
On/Power Down Reset threshold, refer to the electrical characteristics of the datasheet.
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