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AN1772 - APPLICATION NOTE

INTEGRATED RESET CIRCUITS

Integrated Reset Circuits, like the STM809-812, are devices that are dedicated for reset and monitoring

purposes. They monitor the input voltage supply and send a reset signal to the microprocessor for a preset

time interval, if the voltage supply goes outside the preset limit.

A typical reset device consists of a voltage reference, a voltage comparator, a supply voltage resistor-di-

vider network, a fixed delay time circuit and an output driver (see Figure 3).

The internal voltage comparator monitors the input voltage supply and compares it with a predefined volt-

age reference. If the supply voltage is under the threshold, a reset signal RST, is asserted. The signal re-

mains asserted until the supply voltage reaches the threshold and stays above it for a preset time interval.

The output of the Reset Circuit is independent of the Power-up slew rate, glitches and other brownout con-

ditions.

Figure 3. Integrated Reset Circuit

Note: 1. STM811/812 only.

AI08627

COMPARE

DEBOUNCE

Delay

MR

(1)

RST

Output