© Semiconductor Components Industries, LLC, 2003

September, 2003 − Rev. 1

1

Publication Order Number:

AND8116/D

AND8116/D

Integrated Relay/Inductive

Load Drivers for Industrial

and Automotive

Applications

Prepared by: Alejandro Lara

ON Semiconductor

Abstract

Most PC

board

mounted

relays

are

driven

by

microprocessors or other sensitive electronic devices. A

successful coil drive circuit requires isolation between the

relay and the microprocessor circuitry. Effective drive

circuits must account for drive current and voltage

requirements as well as effective suppression of L di/dt

transients which can destroy microprocessor circuits. While

it is easy to over−design an effective drive circuit, today’s

designs must be cost competitive. Integrating a monolithic

IC driver device into the relay will provide significant value

to the system designer.

This

paper

describes

the

operation

of

ON Semiconductor’s integrated relay driver products to

interface sensitive electronic devices with mechanical

relays to accomplish different control/power functions.

Important benefits such as PC board space savings and

components count reduction are also explained.

Introduction

Although the advances in the electronics industry are

increasing day by day, mechanical relays are still

extensively used in industrial and automotive applications to

control high current loads. Their low cost and excellent fault

tolerance make relays to be an useful and reliable solution

in industrial and automotive applications environments. The

integrated relay driver devices NUD3105, NUD3112 and

NUD3124 offered by ON Semiconductor are considered to

be the ideal device solution to control mechanical relays

used in industrial and automotive applications. Their

integrated design allows significant simplification and cost

reductions when replacing traditional discrete solutions

such as bipolar transistors plus free−wheeling diodes.

Industrial and Automotive Application Requirements

The device requirements for industrial and automotive

applications are different and must be addressed in different

manner. While the requirements for automotive applications

are the most difficult to comply with, industrial

requirements traditionally allow more latitudes. Relay coil

currents vary considerably depending on the applications.

The largest class of industrial and automotive relays have

coils with current consumption between 50 and 150 mA.

Selection of a suitable relay driver requires many

constraints to be evaluated. For automotive applications, it

is necessary to put special attention in the following

requirements:

Meeting these automotive requirements usually results in

specifying an oversized and non−cost effective relay driver,

or one requiring many protection components.

Industrial applications on the other hand do not have many

requirements different than the standard ones such as ESD

immunity (usually 2.0 kV HBM), and a given range of

operating ambient temperature (usually between 0

°C to

85

°C). However, some applications also call for protection

devices against transient voltage conditions, which creates

the need for extra protection components too.

APPLICATION NOTE

http://onsemi.com