© 1999 Microchip Technology Inc.

Preliminary

DS11187D-page 3

MCP100/101

FIGURE 1-1: MCP100/101 Timing Diagram

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

momentarily, and the second, is when a slowly decay-

ing power supply causes the microcontroller to begin

executing instructions without enough voltage to sus-

tain 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 dura-

tion vs. reset comparator overdrive for which the

MCP100/101 will not generate a reset pulse. 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 cap mounted as

transient immunity.

FIGURE 2-2: Typical Transient Response

RESET

RESET

(MCP100)

(MCP101)

MICROCONTROLLER

MCLR

RST

MCP100

OR

RESET

VSS

bypass

capacitor

TIME

0

0

5V

012

3

10

8

6

4

2

0

45

Transients above the

curve will cause a reset

Transients below

the curve will NOT

cause a reset

11187d.book Page 3 Friday, September 10, 1999 8:52 AM