Datasheet

DocID028794 Rev 4 21/224
STM32L433xx Functional overview
55
• V
BAT
= 1.55 to 3.6 V: power supply for RTC, external clock 32 kHz oscillator and
backup registers (through power switch) when V
DD
is not present.
Note: When the functions supplied by V
DDA
or V
DDUSB
are not used, these supplies should
preferably be shorted to V
DD
.
Note: If these supplies are tied to ground, the I/Os supplied by these power supplies are not 5 V
tolerant (refer to
Table 19: Voltage characteristics).
Note: V
DDIOx
is the I/Os general purpose digital functions supply. V
DDIOx
represents V
DDIO1
, with
V
DDIO1
= V
DD
.
Figure 2. Power supply overview
3.9.2 Power supply supervisor
The device has an integrated ultra-low-power brown-out reset (BOR) active in all modes
except Shutdown and ensuring proper operation after power-on and during power down.
The device remains in reset mode when the monitored supply voltage V
DD
is below a
specified threshold, without the need for an external reset circuit.
The lowest BOR level is 1.71V at power on, and other higher thresholds can be selected
through option bytes.The device features an embedded programmable voltage detector
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