Designing With the SN74LVC1G123 Monostable Multivibrator - SLVA720A - Application Guide

Oct 12, 2026

Discusses how monostable multivibrators operate and where they can be applied, using the SN74LVC1G123 as the example device while noting that Texas Instruments offers functionally similar parts across other logic families. Explains stable and unstable states, key terminology such as pulse width and retriggering, and the RC time-constant basis behind fixed-duration output pulses. Covers practical uses including debouncing, pulse extension, delays, and edge detection, with supporting theory and device context.

LanguageEnglish

CategoryTechnology

FormatPDF

Pages10

Reading Time25 min

AccessFree to download

1 Introduction

2 Terminology

3 Theory of Operation

3.1 Basic Concept

3.2 Operation

4 Applications

5 Frequently Asked Questions

6 Revision History

Application Report Designing With the SN74LVC1G123 Monostable Multivibrator Emrys Maier HVAL – Standard Linear and Logic ABSTRACT This document discusses the operation of and applications for monostable multivibrators. The SN74LVC1G123 was chosen as the example device, but Texas Instruments has a wide variety of other monostable multivibrator devices in other logic families that operate in practically the same manner. The applications here can be applied to almost any monostable multivibrator. Table of Contents 1 Introduction.............................................................................................................................................................................2 2 Terminology.............................................................................................................................................................................2 3 Theory of Operation................................................................................................................................................................2 4 Applications............................................................................................................................................................................ 4 5 Frequently Asked Questions................................................................................................................................................. 9 6 Revision History......................................................................................................................................................................9 SLVA720A – JULY 2015 – REVISED OCTOBER 2020 Designing With the SN74LVC1G123 Monostable Multivibrator 1 Submit Document Feedback Copyright © 2020 Texas Instruments Incorporated 1 Introduction A “Monostable Multivibrator” is so named because its output is only stable in one state. When triggered, this device will switch the output to the so-called 'unstable state' for a set period of time and then return to the stable state. Note that "stable" in this context refers to an output state that will remain the same without an external input and "unstable" refers to a state which will change without external input. Since one input trigger event results in one output pulse, this device is also known as a “one-shot.” The SN74LVC1G123 will be used herein as an example because it is one of our most popular devices, but TI offers many other monostable multivibrators in different logic families to fit a wide variety of applications. These devices can be used as debouncers, pulse extenders, delays, and edge detectors. They are very useful for cleaning up input signals to logic circuits of all types. 2 Terminology • Stable State – The natural, resting, or ‘off’ state of a monostable multivibrator’s output; usually ‘low’ • Unstable State – The temporary, active, or ‘on’ state of a monostable multivibrator’s output; usually ‘high’ • Pulse Width – The amount of time for which the output is switched. Often referred to as ‘tw’ • Trigger – The input signal edge which causes an output pulse to be generated. The trigger can be on a rising or falling edge depending on which input is used. • Retrigger – The act of applying a trigger signal while the output of the system is already in the unstable state. • Retriggerable-A monostable multivibrator that has the capability to retrigger. 3 Theory of Operation 3.1 Basic Concept Any monostable multivibrator that has an external RC circuit for timing will operate on the same basic principle. The capacitor in an RC circuit will take a set amount of time, referred to as the ‘time constant,’ to charge up to 63.2% of its full charge from a fully discharged state. It takes 5 time constants to reach 99.3% of its full charge, which is generally accepted as a fully charged state. These two values are derived from the RC circuit step response characteristic equation, Eq

FAQs

What is a monostable multivibrator (one-shot) and how does it behave after a trigger?

Its output remains stable in one state until a trigger event occurs. The output switches to an unstable (active) state for a set time and then returns to the stable state.

How do RC time constants determine the pulse width in a monostable multivibrator?

With an external RC timing circuit, the capacitor charges according to the RC step response. The document states it reaches 63.2% of full charge at one time constant and about 99.3% after five time constants, which underpins the timing to switch the output.

What are common real-world applications of monostable multivibrators?

They can be used as debouncers, pulse extenders, delays, and edge detectors to help clean up input signals for logic circuits.

Oct 12, 2026

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