Reset And Power-Supply Supervisor; Brownout Reset (Bor); System Reset; Figure 6. Brownout Reset Waveform - ST STM32U575 Series Application Note

Example of computation of the energy provided to the MCU during the power-down phase
If the sum of decoupling capacitors on V
energy remaining in the decoupling capacitors is:
2
E = ½ C x V = ½ x 10
The energy remaining in the decoupling capacitors is below 1 mJ, so it is acceptable for the MCU to absorb it.
2.4

Reset and power-supply supervisor

2.4.1

Brownout reset (BOR)

The devices have a Brownout reset (BOR) circuitry. The BOR is active in all power modes except Shutdown
mode, and cannot be disabled. The BOR monitors the Backup domain supply voltage, that is V
V otherwise.
BAT
Five BOR thresholds can be selected through option bytes.
During power-on, the BOR keeps the device under reset until the supply voltage V
threshold. When V
V upper limit, the device reset is released and the system can start.
BORx
For more details on the Brownout reset thresholds, refer to the electrical characteristics section in the datasheet.
2.4.2

System reset

A system reset sets all registers to their reset values except the reset flags in RCC_CSR register and the
registers in the Backup domain.
A system reset is generated when one of the following events occurs (refer to reference manual for more details):
• a low level on the NRST pin (external reset)
• a window watchdog event (WWDG reset)
• an independent watchdog event (IWDG reset)
• a software reset
• a low-power mode security reset
• an option byte loader reset
• a Brownout reset
These sources act on the NRST pin, that is always kept low during the delay phase. The reset service routine
vector is selected via the boot option bytes.
AN5373 - Rev 1
DDX
-5 2
x 3.3 = 0.05 mJ
drops below the selected threshold, a device reset is generated. When V
DD
Figure 6.
V
DD
V (rising edge)
BOR
V (falling edge)
BOR
Reset
(1) The reset temporization t
is 10 μF and V drops below 1 V while V
DD
Brownout reset waveform
Hysteresis
t
RSTTEMPO
temporization (1)
is present only for the BOR lowest threslhold (V
RSTTEMPO
AN5373
Reset and power-supply supervisor
is still at 3.3 V, the
DDX
when present,
DD
reaches the specified V
DD
is above the
DD
)
BOR0
page 12/37
BORx