ST STM32F412 Reference Manual page 88

Power controller (PWR)
To allow the RTC to operate even when the main digital supply (V
pin powers the following blocks:
•
The RTC
•
The LSE oscillator
•
PC13 to PC15 I/Os
The switch to the V
block.
Warning:
If no external battery is used in the application, it is recommended to connect the V
V with a 100 nF external decoupling ceramic capacitor in parallel.
DD
When the backup domain is supplied by V
following functions are available:
•
PC14 and PC15 can be used as either GPIO or LSE pins
•
PC13 can be used as a GPIO or additional functions can be configured (refer to
Table 27: RTC additional functions
Note: Due to the fact that the switch only sinks a limited amount of current (3 mA), the use of
PC13 to PC15 GPIOs in output mode is restricted: the speed has to be limited to 2 MHz with
a maximum load of 30 pF and these I/Os must not be used as a current source (e.g. to drive
an LED).
When the backup domain is supplied by V
V is not present), the following functions are available:
DD
•
PC14 and PC15 can be used as LSE pins only
•
PC13 can be used as the RTC additional function pin (refer to
functions
88/1163
supply is controlled by the power-down reset embedded in the Reset
BAT
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 V
support this current injection, it is strongly recommended to
connect an external low-drop diode between this power
supply and the V
for more details about this pin configuration)
RM0402 Rev 6
(temporization at V
DD
.
is established in less than
DD
+ 0.6 V, a current may be injected into V
).
BAT
pin.
BAT
(analog switch connected to V
DD
for more details about this pin configuration)
(analog switch connected to V
BAT
) is turned off, the V
DD
startup) or after a PDR
and V remains
BAT DD
RSTTEMPO
BAT
and the
DD
pin cannot
BAT
BAT
), the
DD
because
BAT
Table 27: RTC additional
RM0402
BAT
)
pin to