RM0033 Rev 9 69/1381
RM0033 Power control (PWR)
83
4.2.2 Brownout reset (BOR)
During power on, the Brownout reset (BOR) keeps the device under reset until the supply
voltage reaches the specified V
BOR
threshold.
V
BOR
is configured through device option bytes. By default, BOR is off. Three
programmable V
BOR
threshold levels can be selected:
BOR Level 3 (V
BOR3
). Brownout threshold level 3.
BOR Level 2 (V
BOR2
). Brownout threshold level 2.
BOR Level 1 (V
BOR1
). Brownout threshold level 1.
Note: For full details about BOR characteristics, refer to Section “Electrical characteristics" in the
device datasheet.
When the supply voltage (V
DD
) drops below the selected V
BOR
threshold, a device reset is
generated. The BOR can be disabled by programming the device option bytes. Therefore,
the power-on and power-down is then monitored by the POR/ PDR (see Section 4.2.1:
Power-on reset (POR)/power-down reset (PDR)).
The BOR threshold hysteresis is ~100 mV (between the rising and the falling edge of the
supply voltage).
Figure 6. BOR thresholds
4.2.3 Programmable voltage detector (PVD)
You can use the PVD to monitor the V
DD
/V
DDA
power supply by comparing it to a threshold
selected by the PLS[2:0] bits in the PWR power control register (PWR_CR).
The PVD is enabled by setting the PVDE bit.
A PVDO flag is available, in the PWR power control/status register (PWR_CSR), to indicate
if V
DD
/V
DDA
is higher or lower than the PVD threshold. This event is internally connected to
the EXTI line16 and can generate an interrupt if enabled through the EXTI registers. The
PVD output interrupt can be generated when V
DD
/V
DDA
drops below the PVD threshold
and/or when V
DD
/V
DDA
rises above the PVD threshold depending on EXTI line16
rising/falling edge configuration. As an example the service routine could perform
emergency shutdown tasks.
V
DD
/V
DDA
Reset
100 mV
hysteresis
BOR threshold
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