STMicroelectronics STM32F05 series User Manual

Power control (PWR) RM0091
68/742 Doc ID 018940 Rev 1
When V
DDA
is different from V
DD
, it must always be higher or equal to V
DD
. In order to
ensure this condition, also during power-up/power-down transitions, an external Shottky
diode may be used between V
DD
and V
DDA
.
6.1.2 Battery backup domain
To retain the content of the Backup registers and supply the RTC function 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 powers the RTC unit, the LSE oscillator and the PC13 to PC15 IOs, allowing
the RTC 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 may 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 V
BAT
pin cannot
support this current injection, it is strongly recommended to
connect an external low-drop diode between this power
supply and the V
BAT
pin.
If no external battery is used in the application, it is recommended to connect V
BAT
externally to V
DD
with a 100 nF external ceramic decoupling capacitor (for more details refer
to AN2586).
When the backup domain is supplied by V
DD
(analog switch connected to V
DD
), the
following functions are available:
● PC13, PC14 and PC15 can be used as GPIO pins
● PC13, PC14 and PC15 can be configured by RTC or LSE (refer to Section 24.3: RTC
functional description on page 536)
Note: Due to the fact that the switch only sinks a limited amount of current (3 mA), the use of
GPIOs PC13 to PC15 in output mode is restricted: the speed has to be limited to 2 MHz with
a maximum load of 30 pF and these IOs must not be used as a current source (e.g. to drive
an 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 or LSE (refer to Section 24.3:
RTC functional description on page 536)

STMicroelectronics STM32F05 series Specifications

General

Brand	STMicroelectronics
Model	STM32F05 series
Category	Microcontrollers
Language	English