AN4467 datasheet(14/33 Pages) STMICROELECTRONICS

14 / 33 page

Power supplies

AN4467

14/33

DocID026156 Rev 2

1.3.1

Power-on reset (POR) / Power-down reset (PDR),

Brownout reset (BOR)

The monitoring voltage begins at 0.7 V.

During power-on, for devices operating between 1.8 and 3.6 V, the BOR keeps the device

under reset until the supply voltages (VDD and VDDA) come close to the lowest acceptable

voltage (1.8 V). At power-up this internal reset is maintained during ~ 1 ms to wait for the

supply to reach its final value and stabilize.

At power-down the reset is activated as soon as the power drops below the lowest limit (i.e.

1.65 V).

At power-on, a defined reset should be maintained below 0.7 V. The upper threshold for a

reset release is defined in the electrical characteristics section of the product datasheets.

Figure 5. Power on reset/power down reset waveform

For a programmable threshold above the chip lowest limit, a brownout reset can be

configured to the desired value. The BOR can also be used to detect a power voltage drop

earlier. The threshold values of the BOR can be configured through the FLASH_OBR option

byte.

1.3.2

Programmable voltage detector (PVD)

The device features an embedded programmable voltage detector (PVD) that monitors the

VDD/VDDA power supply and compares it to the VPVD threshold. Seven different PVD levels

can be selected by software between 1.85 and 3.05 V, with 200 mV steps.

An interrupt can be generated when VDD/VDDA drops below the VPVD threshold and/or when

it’s higher than the VPVD threshold. The interrupt service routine then generates a warning

message and/or puts the MCU into a safe state.

The PVD is enabled by software configuration. As an example, the service routine can

perform emergency shutdown tasks.

AN4467 Datasheet(PDF) 14 Page - STMicroelectronics