Battery Backup Domain - ST STM32F101 Series Reference Manual

Power control (PWR)
On 100-pin packages
To ensure a better accuracy on low voltage inputs, the user can connect a separate external
reference voltage ADC input on V
2.4 V to V
On packages with 64 pins or less
The V
REF+
voltage supply (V
3.1.2

Battery backup domain

To retain the content of the Backup registers and supply the RTC function when V
turned off, V
by another source.
The V
BAT
the RTC to operate even when the main digital supply (V
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, V
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 GPIO, TAMPER pin, RTC Calibration Clock, RTC Alarm or
second output (refer to
Note: Due to the fact that the switch only sinks a limited amount of current, the use of GPIOs PC13
to PC15 is restricted: only one I/O at a time can be used as an output, 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
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 TAMPER pin, RTC Alarm or Second output (refer to section
Section 9.5.2: RTC clock calibration register (BKP_RTCCR) on page
34/501
.
DDA
and V pins are not available, they are internally connected to the ADC
REF-
) and ground (V
DDA
pin can be connected to an optional standby voltage supplied by a battery or
BAT
pin powers the RTC unit, the LSE oscillator and the PC13 to PC15 IOs, allowing
During the
t
switch between V
V rises fast and may become established during this time,
DD
a current may be injected into V
connected between V
.
− 0.6V
V Refer to the datasheet for the value of
DD
Section 9: Backup registers (BKP) on page
and V . The voltage on V
REF+ REF-
).
SSA
temporization at V
RSTTEMPO
and V remains connected to V
BAT DD
and V
DD BAT
must be connected externally to V
BAT
(analog switch connected to V
DD
(analog switch connected to V
BAT
can range from
REF+
) is turned off. The switch to the
DD
startup, the power
DD
through a diode
BAT
when V is lower than
BAT
t
RSTTEMPO.
132)
133).
RM0008
is
DD
. As
BAT
.
DD
), the
DD
because
BAT