STMicroelectronics STM32WL5 Series Reference Manual page 232

Power control (PWR)
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 supply is controlled by the power-down reset embedded in the reset block.
BAT
Warning:
If no external battery is used in the application, it is recommended to connect VBAT
externally to V
When the backup domain is supplied by V
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)
(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
V is not present), the following functions are available:
DD
•
PC13, PC14 and PC15 can be controlled only by RTC, TAMP or LSE (refer to
Section 32: Real-time clock (RTC)
(TAMP))
•
PA0/TAMP_IN2 and PB3/TAMP_IN3, when they are configured by the TAMP as
tamper pins
Backup domain access
After a system reset, the backup domain (RTC and TAMP backup registers) is protected
against possible unwanted write accesses. The DBP bit must be set in the
register 1 (PWR_CR1)
232/1450
During
t
RSTTEMPO
is detected, the power switch between V
connected to V
BAT
During the startup phase, if V
t (refer to the datasheet for the value of t
RSTTEMPO
and V > V
DD BAT
through an internal diode connected between V
power switch (V
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.
with a 100 nF external ceramic decoupling capacitor.
DD
to enable access to the backup domain
RM0453 Rev 5
(temporization at V
DD
.
is established in less than
DD
+ 0.6 V, a current can be injected into V
).
BAT
(analog switch connected to V
DD
and Section 33: Tamper and backup registers
(analog switch connected to V
BAT
and Section 33: Tamper and backup registers
startup) or after a PDR
and V remains
BAT DD
RSTTEMPO
BAT
and the
DD
), the
DD
because
BAT
PWR control
RM0453
)