MCP120/130

DS11184D-page 4

 2001 Microchip Technology Inc.

2.0

APPLICATIONS INFORMATION

2.1

The Need for Supervisory Circuits

For many of today’s microcontroller applications, care

must be taken to prevent low power conditions that can

cause many different system problems. The most com-

mon causes are brown-out conditions where the sys-

tem supply drops below the operating level momentar-

ily, and the second, is when a slowly decaying power

supply causes the microcontroller to begin executing

instructions without enough voltage to sustain SRAM

and producing indeterminate results.

Figure 2-1:

Typical Application

2.2

Many system designers implementing POR circuits are

concerned about the minimum pulse width required to

cause a reset. Figure 2-2 shows typical transient

duration. It shows that the farther below the trip point

the transient pulse goes, the duration of the pulse

required to cause a reset gets shorter. A 0.1

µF bypass

vides additional transient immunity.

Figure 2-2:

Typical Transient Response

Microcontroller

MCLR

RST

MCP120

or

RESET

Bypass

Capacitor

TIME

0

0

5V

MAX

MIN

Transient

Duration

MIN

01

23

10

8

6

4

2

0

45

Transients above the

curve will cause a reset

Transients below

the curve will NOT

cause a reset