ST STM32WL5 Series User Manual

RM0453 Rev 1 223/1461
RM0453 Power control (PWR)
276
6.1.2 Battery Backup domain
To retain the content of the backup registers and supply the RTC and TAMP functions when
V
DD
is turned off, the VBAT pin can be connected to an optional backup voltage supplied by
a battery or by another source.
The VBAT pin powers RTC, TAMP, the LSE oscillator and the PC13 to PC15 I/Os, allowing
RTC and TAMP to operate even when the main power supply is turned off. The switch to the
V
BAT
supply is controlled by the power-down reset embedded in the reset block.
Warning: During t
RSTTEMPO
(temporization at V
DD
startup) or after a PDR
is detected, the power switch between V
BAT
and V
DD
remains
connected to V
BAT
.
During the startup phase, if V
DD
is established in less than
t
RSTTEMPO
(refer to the datasheet for the value of t
RSTTEMPO
)
and V
DD
> V
BAT
+ 0.6 V, a current can be injected into V
BAT
through an internal diode connected between V
DD
and the
power switch (V
BAT
).
If the power supply/battery connected to the VBAT pin cannot
support this current injection, it is strongly recommended to
connect an external low-drop diode between this power
supply and the VBAT pin.
If no external battery is used in the application, it is recommended to connect VBAT
externally to V
DD
with a 100 nF external ceramic decoupling capacitor.
When the Backup domain is supplied by V
DD
(analog switch connected to V
DD
), the
following pins are available:
• PC13, PC14 and PC15, that can be used as GPIO pins
• PC13, PC14 and PC15, that can be configured by RTC, TAMP or LSE (refer to
Section 32: Real-time clock (RTC) and Section 33: Tamper and backup registers
(TAMP))
• PA0/TAMP_IN2 and PB3/TAMP_IN3 when they are configured by the TAMP as tamper
pins
Note: Due to the fact that the analog switch can transfer only a limited amount of current (3 mA),
the use of GPIO PC13 to PC15 in output mode is restricted: the speed must be limited to
2
MHz with a maximum load of 30 pF and these I/Os must not be used as current source
(e.g. to drive a LED).
When the Backup domain is supplied by V
BAT
(analog switch connected to V
BAT
because
V
DD
is not present), the following functions are available:
• PC13, PC14 and PC15 can be controlled only by RTC, TAMP or LSE (refer to
Section 32: Real-time clock (RTC) and Section 33: Tamper and backup registers
(TAMP))
• PA0/TAMP_IN2 and PB3/TAMP_IN3, when they are configured by the TAMP as
tamper pins

ST STM32WL5 Series Specifications

General

Brand	ST
Model	STM32WL5 Series
Category	Microcontrollers
Language	English