MCP120T データシートの表示（PDF） - Microchip Technology

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MCP120T

Microcontroller Supervisory Circuit with Open Drain Output

Microchip Technology 

MCP120/130

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.

VDD

MCP120

VDD

Microcontroller

VDD

Bypass

Capacitor

VSS

RST

MCLR

or

RESET

VSS

Figure 2-1: Typical Application

2.2 Negative Going VDD Transients

Many system designers implementing POR circuits are

concerned about the minimum pulse width required to

cause a reset. Figure 2-2 shows typical transient

voltage below the trip point (VTRIP - VDD) vs. 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

cap mounted as close as possible to the VDD pin pro-

vides additional transient immunity.

5V

Transient

Duration

0

0

VTRIPMAX

VTRIPMIN

(VTRIPMIN - VDD)

TIME

10

TA = +25°C

8

6

Transients above the

4

curve will cause a reset

2 Transients below

the curve will NOT

cause a reset

0

0

1

2

3

4

5

VTRIP - VDD (V)

Figure 2-2: Typical Transient Response

DS11184D-page 4

 2001 Microchip Technology Inc.

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