,WILLIAMS GEOFF

• Provides step-by-step instructions for building your own CNC mochine

• Greot for use os ⁰ teoching tool in metol/wood shop or on the industriol floor

GEOFF

, WILLIAMS

(J

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CNC Robotics

Build Your Own Workshop Bot

Geoff Williams

McGraw-Hili

New York Chicago San Francisco Lisbon London Madrid Mexico City Milan New Delhi San Juan Seoul

Singapore Sydney Toronto

. /

Cataloging-i n-Publication Data is on file with the Library of Congress

Copyright

2003 by The McGraw-Hili Companies, Inc. All rights reserved. Printed in the United States of America. Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a data base or retrieval system, without the prior written permission of the publisher.

3 4 5 6 7 8 9 0 DOC!DOC 0 9 8 7 6 5 4 ISBN 0-07-141828-8

The sponsoring editor for this book was Judy Bass and the production supervisor wa s Pamela Pelton. It was set in Tiepolo Book by Patricia Wallenburg.

Printed and bound by RR Donnelly.

McGraw-Hili books are available at special quantity discounts to use as premiums and sales promotions, or for use in corporate training pro- grams. For more information, please write to the Director of Special Sales, McGraw-Hili Professional, Two Penn Plaza, New York, NY 10121-2298 . Or contact your local bookstore.

II\ Thi s book is printed on recycled, acid-free paper containing a

\:CI minimum of 50 percent recycled, de-inked fiber.

Information contained in this book has been obtained by The McGraw-Hili Companies, Inc. ("McGraW-Hili") from sources believed to be reliable.

However, neither McGraw-Hili nor its authors guarantee the accuracy or completeness of any information published herein, and neither McGraw-Hili nor its authors shall be responsible for any errors, omissions,or damages arising out of use of this information.This work is published with the under- standing that McGraw-Hili and its authors are supplying information but are not attempting to render engineering or other professional services.Ifsuch services are required, the assistance of an appropriate professional should be sought.

For Margaret, whose help and patience made this book possible.

I "

I

I - I I

I 1,,1

Contents

1 Design 1

Why Build My Own I

Gantry Style 2

Motors 2

Lineal Motion 4

Motor Drivers 9

Acme Screw 9

Deciding on the Dimensions of the Machine 9

Software 10

2 Electronics 13

Stepper Motor Driver and Computer Interface Boar ds 13

Stepper Motor Driver Circuit 15

The Interface Board 19

3 Making the Printed Circuit Board 77

Tools and Material ₇₇

Artwork 78

Board Cutting and Cleaning 82

Toner Transfer 85

Etching 93

4 Driver Assembly 99

The Interface Board III

v

GNG Robo tics

5 Softwa re Setup and Driver Testing 113

Material Needed 1 13

Creating Test Files 121

Triangle Test 122

Circle Test 123

Putting th e Elect ro nics in a Case 124

6 The Frame 13 3

Tools and Ma teria l 133

Bolting 138

Assemb ly 14 1

Bearing Ra il S upport Bolt Holes 144

Paint the Frame 151

7 The G antry and X-axis 1 53

T he Ga ntry 153

The X-ax is: Ins ta ll i ng t he Gantry Bearing Guide Rail 160

Beari ng Holder 164

8 The Z and Y Axes 175

T he Z-Axis 175

The Y-Axls 184

9 Motor and Lead Screw Insta llat ion 1 8 9

Tools and Ma teria l 189

X-axis 190

Y-axls 199

Z-axis 203

Lim it Switc h Install at ion 206

X -axis Li mi ts 208

Y-axis Limi ts 209

Z-axis Li mits 211

10 File Creation and KCam 215

KCam CNC Cont rol ler Software 215

KCam File Require me nts 219

How to Create a File to Import 222

CorelDraw 223

ACME Prof ile r 239

vi

Contents

11 Tool Holders and Testing 245

Tool Holders 245

Penholder Tool 246

Router/Dremel Holder 252

Testing the CNC Machin e 257

12 Examples 263

Plotter 263

Mechanical Engraving Tool 268

Dremel Tool 271

Ma ster Craft Rotar y Tool 274

Router 278

Sources of M aterial 293

Electronic Components 293

L297 /L298 Integrated Circuits 293

CANADA 293

United States, California 294

Lineal Motion 296

Distributor 296

Manufacturers 29 7

Stepper Motors 300

Metal 301

Index 303

vii

Acknowledgments

I must t ha nk my brother Karl who in spi red me to write this book and my editor Judy Bass w ho se fa ith and assistance made th e book a rea l- ity. I'd al so like to thank P atric ia Wallenburg w ho asse mbled my words and ima ges into book form . Judy an d Patr icia have made this book project an extre me ly enjoyabl e expe rien ce. Finally my tha nks go ou t to a ll the people w ho have freely shared w ith me thei r know ledge a nd assistance wh ile I was resea rchi ng and .bui lding my CNC machi ne.

I must t hank the following co mpan ies for a llowing me to include some of their cop yrighted materia l in this book.

The NuArc Company, Inc. does n' t p romot e, endo rse . or wa rra nty an y modified product s. NuArc le t me reproduce so me of the imag es from t he repair ma nua l of th e copy came ra I disassembled but they don 't endorse th e use of thei r p roducts for anything ot her t ha n the ir origi- nally intended fu nction. You can co nta ct NuArc at M&R Sa les a nd Service, Inc. I N. 372 Main Street , Glen Ellyn, IL 60 1 3 7, USA or on the Web at http :/ / w ww.nua rc.com.

Kellywa re ha s allo wed me to use sc ree n ca ptures of the progra m K Ca m 4. K e llywa re ca n be contacted at PO Box 563 . Spirit L a ke. Iowa 52 36 0 , USA or on the web at http:/ / www.kellyware.co m.

The product data she et s included w ith Chapter 2 of th is book ha ve been reprinted with the pe rm iss ion of STMicroelectron ics . The docu- ments reproduced in th is book and many more us eful app lication notes ca n be found at th e STMic roe lectron ics Web site loca ted at http:/ / www.st. co m.

Scien ce Speciali st s, Inc. ha s give n me per miss ion to include sc ree n captures of th e softw a re A CME Profller, Coyot e Version 6. 0. Scien ce Spec iali sts, Inc. ca n be rea ched at 1800 Shec kle r Rd.. Columbia City, IN 4675, USA or on th e Web at http t/ zwwwzfw t.co m/ v. klmble/

sc ispec/scispec. htm .

Design

Why Build My Own

I first th ought about adding a CNC ro uter to my too l collectio n after fi nis hing a kitch en cab inet renovatio n in my home. I refaced the cabinets and bui lt 26 new doors. during whic h I discovered that door buildi ng can becom e mo noto nou s at best. As a lways hap pens w hen yo u tell or show yo ur fri ends and fam il y w hat yo u have d on e, som eone w i ll have a sim ilar p ro ject and enlist yo ur help . Tha t someone was m y frie nd Geoff S. He wanted to do the same thing to his kitchen-reface and install new cabinet doors. I agreed to help him and he decided on a style of doo r that can be ma de f rom one piece of ma terial cut to size and routed to create th e look he wanted . Of cou rse the prospect of bu il ding a w ho le Jot of doo rs and making temp lates to faci litate the routi ng was n't too thrilling. That's w hen I t ho ught a sma ll CNC m achine wo uld co me in han dy. A ll th e repeti ti ve rou tin g cou ld be asslg ned to the CNC mach ine and t he doors w ou ld more closely resemble each other o nce human erro r had been removed from t he equation . Now the project didn't seem too bad at all!

I started to look for an affordable machine to do the job, After searching t he Intern et , I was shocked to find how mu ch the asking pri ce is fo r a CN C mach ine. I did fi nd a cou ple that were under

1

CNC R obotics

56000 U.S., bu t I ca n never co nv ince myse lf to b uy a too l wo rth so much . Even if the cost of th e ma chin e seems reasona ble you st ill have ship ping a nd du ties to pay, and in my case t he exc ha nge ra te be twe en U.S. and C a na dian dolla rs. All things considered, it was going to cost me in excess of 510,000 C anad ian to get a CNC ma ch ine in my shed . I can 't afford that kind of pr ice tag! I sea rched for plans or a book that described what I wanted to bui ld. I did find some plans on the Internet but either t he machine was too sma ll and inaccurate or the plans were expensive and requ ired the use of expensive components. I cou ldn 't find any books in print about a similar project. I won't buy p lans t hat I can't get a good look at first , so the Inte rnet plans were out of t he qu estion. I prefer books bec a use I ca n hold them and flip through t he pages before I hand ove r th e cas h. Books also cost less.

I decide d to b uild my ow n ma ch ine us ing some off-t he -she lf linea l mot ion co mpo ne nts a nd so me co mpone nts tha t I salvaged o r modified to suit the project . I thou gh t t he most logica l t hing wo uld be to docum ent my p rogress a nd share th e inform a tion t hrough a book . To s um ma rize, I deci ded to build my ow n ma chin e because I love a cha llenge a nd I learn mo re whe n I have a pra cti- ca l proje ct; a lso, I ca n keep th e cost low. It's that simple.

Gantry Style

In my op inion , a gantry styled CNC mach ine is sim plest to imp le- ment. A few years ago , I built a ba nd saw mill fram e and gantry, so th e d esign of a more accura te syste m didn' t seem too to ugh a p ro ject. I a lso like the idea of moving th e tool over the material ra th er tha n the mat er ial under the tool. A mach ine built to move ma teria l would not have as la rge a wo rking a rea for a given foot- pri nt. Con s idering my work shed is only 22 X 12 feet , a gantry mach ine is most suitable.

Motors

The first purchase to make was the stepper motor. My loca l Princess Auto h as a grea t surplus department, so I headed there 2

1 - - - - - - - - - - - - - - - - - - - - - - - -

I

Chapter 1 / D esign

first. Sure enoug h, they had some step- syn motors (seen in Fi g u res 1.1 and 1.2) . They are Nema frame size 34 , draw 1.4 amps per cha n nel, and have a ra ting of 4.6 volt s.

LOT NO. 8201 U' ~

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Figure 1,1

Ste p-Synstepper motor sideview.

Figure 1.2

Step-Syn ste pper motor

top view .

3

CNC Robotics

These motors we re used in an IBM produ ct -probabl y a pr inter.

They are unipolar, b ut if yo u run th em as bipolar the y prod uce more to rqu e (see Figure 1.3).

1 also disco vered that t hese steppe r motors w ork better if t hey are given 12 vo lts ins tead of the 4.6-volt ratin g on th e motor bo dy. The strength of a stepper motor is rated in ou nce inches of holding torque. The ste p-sy n information 1 fo und ind ica te d tha t these mo tor s ar e an ywhere from 90 to 220 ounce inch es. I so metimes wo rk ba ckward s, and bu ying the motors first is ce rta inly just th at ! No rma lly, yo u would calculate w ha t stre ngt h of motor yo u nee d to run th e machine and then purc ha se a s uita b le motor. He re's how to calculate the st re ngt h of motor you need to run this mach ine. If you can 't find any surplus mo tor s, in vestigate a company called Pacific Scientific-they ha ve a variety of s teppe r motors and al so make available soft ware for do wnloa d, w hich yo u ca n use to determine the s ize of motor yo u ne ed . Spe a king w ith them , I was impre ss ed w ith how we ll I wa s tr eated, co ns ide ring 1 wo uld o nly need th ree of the ir motors.

R emember that although brand new motors ar e expe ns ive, you kno w the y will w o rk and yo u ca n match t he streng th to the machine . New motors could also speed up t he ma ch ine consider- abl y. When 1 sa y "speed up ," it is important to not e that I am referrin g to trav el s peeds, not cutti ng s peeds . Cutting speeds for most material s will be s low w ith this sty le of machine, rega rdless of whi ch motor yo u choose; you ca n't run a ro ute r thro ug h w ood at 200 inches per minute and ex pect the cut to look good . Cutting speeds of 10 to 30 inch es per minu te define t he ra nge we can expect from th is machine wit h these motor s. A fast er ma chine can be ex pected to travel quickly w hen not cutti ng and slow down when cutti ng through mat erial.

Lineal Motion

There are a va riety of off-the- shelf lineal motion prod ucts , but most of the syst ems w e re too expe nsive for thi s proj ect. Think ing th at it wo uld be useful s o me day. 1acq uired a NuArc co py cam era a few years ago (se e Figure 1.4 ), so 1 took it apart and found it

4

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Chapter 1 / Design

S TEP-SYN 103-820-0240 4.5V 1 .4 AMP 2DEG/S TEP WIRING DIAGRAM

Figure 1 .3 Wiring diagram of a Step-Syn stepper moto r.

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CNC Ro bot ics

Figure 1.4

Ex ploded illustration of the NuArc Model SST 1418 supersonic horizontal camera. Part 21 is the carriage

6

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C hapte r 1 / Design

uses li neal bearings run ning on guide rails to mo ve th e copy board as we ll as the bellows.

Th e slide employed to move th e bellows and cop y board wo uld work we ll as th e y-axis for my CNC machine. And it w as comp let e with beari ngs an d ho lders buil t in to th e sli de, as pictu red in Figures 1.5 and 1.6.

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Figure 1 .5

NuArcCamera, part number82 isthe

guide rail.

7

Figure 1 .6

Closeupof the slide showing the bearings numbered

40

nut numbered 33.

CNC R obotics

Of the eight bearings, I found t hat onl y four were st ill in satisfacto- ry condition fo r use. I decided that the x-a xis could be built in the same ma nner, employing open linea l bearings running on a ra il tha t ha d been drilled and ta pped to allow t he use of s upport bolts.

I al so ch ose to ma ke my own bearing ho lders for th e x- ax is beca use the co st of preb uilt p rod ucts w as mo re t han I co u ld justify. Rail sup - port ma teri al is ava ilable as we ll, but t he cos t of th is prod uct made me believe it wasn't required a nd t hat t he bolts wo uld give the rail e no ug h su pport. I noti ced th a t the copy came ra d idn't have any ext ra s up port u nder the rails. If yo u wanted extra s upport in a pro j- ect like thi s, it co uld be fashioned fro m two pieces of angle iro n w ith a spacer, but the su rface it would be mounted on-conside r- ing the rail would be in con tact with the support-would have to be perfectly flat. As I had no intention of using perfect steel to bu ild this machine, having the bolts pro vide the support meant that they could be adjusted to bring the rail to a flat plane.

Simi lar bearings an d ra ils cou ld be used for t he z-a xls, b ut I decid- ed ins tea d to use a sw iveling TV tray assembly bo ught a t the Hom e Depot. The glides ar e ra ted at 100 Ibs. to ho ld a te levisio n hori zontall y. My p ro ject would use t he glides vert ica lly, so they wo uld be plenty stro ng, w ith la rge ba ll be a rings an d e nough tra v- e l for t he z-a xls. The NuArc ca mera used 3/4 -i nc h bearings and support rails, so I decide d to use th e sa me bear ing and rail size on the x- axis .

8

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Chapter 1 / Design

Motor Drivers

At thi s point in the proj ect 1 had al read y pu rchased motors, so I looked at simple driver so lut io ns. The be st solution was found in th e form of th e 1297 and 1298 integ rated circuits manufactured by ST Microe lec tro nics . The ir Web s ite ha s all the informa tion need- ed to build a bipol ar s teppe r moto r d river using these two inte- grated c ircuits, w hich ar e often refe rred to as "c hips." A dri ver built from these ch ips can ea sily pr ovide th e vo ltag e and amperage needed by the step sy n motors.

Acme Screw

The qu estion of how to move t he gantry and a xes slides was a lso res olved by co st. I had originally co ns ide red using ball screws, but afte r co mpar ing the cos t of the ball screw w it h that of an acme screw, it didn 't ma ke se nse to s pe nd three times a s mu ch on ba ll screws. The ad vantage s to usin g ball screws ar e tha t a sm aller motor ca n be used to move a given load, and wi th a pre load ed nut, t he re is very little ba ckla sh in the system. As mentioned ea rlier in thi s c ha pte r, this is a machine th a t will no t s peed t hro ug h its a s sign ed job s so we can compe ns a te for ba ckla sh in the softw a re.

This means the project ca n be built usin g les s expensive acme screws.

I also had to de cide ho w many turn s per inch to put on the acme sc rew. My experiments w ith r eady rod proved that too man y tu rns made fo r a nnoy ingly s low movem ent and too few turn s redu ce s th e qu al ity of resolution tha t a llows t he machine to make sm all , precise movem ents. 1sett led on a 1/2 -in ch acm e screw with e ig ht turn s per inch, and a 6- foot length with a nut at a co st of $ 135

Canadian. '

Deciding on the Dimensions of the Machine

Earlier in th e cha pte r 1 expla ined tha t I made t he deci sion of ma chine footprint s ize based on the a rea in my wo rks hop.

9

Figure 1. 7

Viewfrom sideof proposedmachine.

CNC Robotics

B ecau se I on ly have a space 12 X 22 feet a nd tools and mate ri- a ls c u rrently occupy mos t of th a t space, my mac hine wo uld o nly be ab out 7 fee t lo ng a nd 4 feet wide. The next step in t his projeci was to ge nerate concept drawings, since I was going to use some of the components fro m the NuArc horizontal camera . The dimensions of the frame e nded up being longer than t he support rails in order to accommodate the bearing holders and the motor mount with a little roo m

spare. The width of the frame is a few inches shorte r than the balance of a 6-foot acme lead screw, after t he length needed for the z- a xis has been cut from it. The follow - ing illustrations are the concept drawings 1 created to guide the co ns tr uctio n of the mac hine. Figure 1.7 is a drawing of t he ma chine fro m the side.

The next illustrati on, Figure 1.8, is the width of the mach ine, viewe d from t he front.

Software

After figur ing out the approximate shape and dimensions and de cid ing on stepper moto rs and drivers, the next questio n was which software to use to control the machine once finished. 1 looked a t a variety of software solutions and , since my level of experience wit h CNC machinery was nonexistent, I wanted a pro - gra m tha t was easy to use. To communicate to the stepper moto rs 10

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how to move so th e tool being used will fo llow the desired path, a p rog ra m is w ritten in G-code and M-code . The G- and M-codes are used to tell t he machine w here to go in the xyx-axes areas of trav- el a nd what to do when it ge ts t here. Very simple programs describing th ings like boxes o r ci rcles are not very comp licated to w rite yourse lf. 1 wa nted software that wo u ld allow me to create my own desig ns in a drawing program like CorelD raw and t hen impo rt the drawi ng a nd a uto matica lly cre a te the necessary G- and M- code file. 1 loo ked at some freeware but was d isa ppointed by the level of d ifficulty to imple me nt t he software and get it doi ng what I wante d. Furt her research revealed software ca lled KCam that would do exactly w ha t was necessa ry. See the screen capt ure from KCam in Figure 1.9.

KCam isn't freewa re, but it ce rtai nly isn 't expensive either at $100 U.S. pe r copy. The fact that KCam is not expensive s ho uld n't lead yo u to be lieve it is in effective softwa re. It is extremely easy to use an d a llows yo u to customize the use of the p rinte r port . KCam will

Figure 1 .8

Front view of mac hine

1 1

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Figure 1 .9

What Kearn looks like.

CNC Roboti cs

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also import H PGL files cr ea ted in Co rel Draw 9 or OX F files created in CAD soft ware like AutoCa d or in CorelDraw 9.

In this c ha pter I sha red design choices fo r my CNC machin e and

t he rea so ns beh ind them, as well as t he choices of stepper motors,

dri vers . an d soft ware. At t his point in the project. we need to start

t hinking abou t t he elec tro nics. th e topic of t he next chapter.

RI R2 R3 R4 R5 R6 4k 4k 4k 4k 4k 4k

Electronics

Stepper Motor Driver and Computer Interface Boards

This chapter deals wit h the design and construction of the elec- tronics required for controlling stepper motors using a computer and Keam soft ware. The requirements for the drivers are based on the step- syn motor purchased in the previous chapter from the surplus department of Princess Auto (see Fig ur e 2.2).

In addition to these surplus motors, I also bought three ne w motors from Pacific Scientific , also mentioned in the pre vious chapter (see Figure 2.3).

Figure 2.1

The finishedboards.

13

Figure 2.2

Step-syn stepper motor.

Fi gure 2.3

PacificScientific

stepper mot or.

14

CNC Robotics

C hapter 2 / Electronics

All the motors draw 1.4 amps pe r chan nel, but t he step-syn mo tors are rate d at 4.5 volts and t he Pacific Scientific mot or can be given a max imum of 170 volts. Alt ho ugh I'm not using Pacific Scientific moto rs in this project, if yo u are unable to find su itable surplus steppers you m ay wish to purchase new ones. WARNING:

The stepper motor driver boards ^{described i} n this chapter can d rive both of these motors, but you can only use up to 36 volts for moto r power-too many volts will fry the L298 integrated circuit. A com - pa ny called ST Microelectronics has gracious ly given me permis- sion to reproduce t he data sheets and app lic at ion notes in their entirety in thi s chapter (see pages 22 through 75). These docu - ments are the basis of th e driver board design . Read them t hor- o ughly to ga in a greater understa nding of the strengths and lim i- ta tions of t he L297/L298 integrated circ uits (referred to as ICs) i n t his app lic ation .

Stepper Motor Driver Circuit

The stepper motor driver boards ar e th e mu scles of the CNC machine.

Th ey receive sig na ls f ro m the co mp uter that in d icate whic h direc- ti on that ax is will travel and how far it wi ll m ove. Th ey are the mu scles becau se as they receiv e direct io n and step signa ls from

Figure 2.4

L297 stepper m otor

controller IC.

Figure 2.5 L298 H Br idge IC.

15

CNC R oboti cs

the computer, they translate the information into higher voltage and amperage signa ls to send to the stepper motors. The power sent to the stepper motor coils is distributed to the coils in a sequence that will move the shaft in the desired direction as ma ny steps as are needed to traverse the distance required on that axis . For th is p roject we need thr ee d river boards. one for each ax is of travel. The boa rds are designed usin g a set of in tegrated circuits manu factured by STMicroelect rion ics- t he L297 and L298 . The nice thing about usin g th ese two chi ps is t hat th e boa rd design is quite simple. o nly req uiring a min ima l number of co mponents. A second benef it is that w hen com bined, these two chips create a very powerful driver boar d capable of handli ng up to 36 vo lts and 2 amperes per channe l. A lot of b ipolar and uniploa r stepper motors currently manufactured or available as surplus. which are strong enough to be used for this machine. are well within the tol- erances of these chips. T he steppers that I decided to use are Sanyo Denki step-syn and are rated at 4 .5 volts and 1.4 amps per c hannel wi t h a resolution of 2 degrees per step. T he power rat ings are well wi th in t he to lera nces of the drive r boa rd. You can refe r to the schemat ic (Figure 2.6) to dete rm ine the co mponents requ ired for this bo ard .

Table 2-1 Part Quantity Description

DriverBoard

U l 1 L298 Dual full-bridge driver

Components

U2 1 L297 Stepper motor controller

Dl-D8 8 FR304 Fast recovery diode

Cl 1 3.3 NF capacitor

C2,C3 2 0.1 UF capacitor

C4 1 470 UF capacitor

C5, C6 2 lNF capacito r

Rl, R 2 2 0 .5 ohm power resi stor

R3 1 lK ohm resisto r

R4 1 22K ohm resis tor

(continued

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H-

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Tl>-

^f-'

^vs

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12 VS GNO 2

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Tl>-

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CNC R obotics

Table 2-1 Part Qu antity Description

Driver Board

R 5 1 2K2 ohm resistor

Components

( contin ued) R 6 1 10K ohm resistor

R 7, R8 2 4 ,7K ohm resisto r

JP1-JP6 3-3pin, 2-4pin C ut to size from header material.

H eat Sink 1 You must inst all a heat sink on the 1.298.

Now for a brief explanatio n of t he circuit ; note t hat I am incl udi ng in this chapter the data sheets fo r t he L298 and L297 ICs as we ll as the applicat ion notes , so yo u will be able to refer to the source mat eria l at will (see pag es 22 through 75). The information con - tained in these documents is essentially a ll you need to create the ci rcui t you are about to b uild .

This ci rcuit works by receiv ing signa ls from the computer 's pa ral- lel po rt to p in 17 o n th e L297 for di rect ion of t he stepper motor and pin 18 on the 1.29 7 fo r t he num ber of steps th e moto r will take in that directi on . The L297 th en sends sig nals to the 1.298 in th e sequence in w hic h the windin gs mu st be powered up to accom- pli sh the task. Then th e 1.298 p rov ides power to th e motor w ind- ings in th e proper o rde r. You will note t hat motor power is sup - plied on ly to the L298 for t his pu rpose. But both chips require + 5 vo lts to fu nction . The eight FR304 d iodes cla mp the stepper motor windings to moto r voltage and ground . Diodes used for this pur- pose must be fast recovery but could be a d ifferent value based on the amperage needed by the stepper motors used. Th is protects the L298 from the in duced high voltages generated by the stepper moto r w hen the any of th e wind ings are turned off.

Pins I an d 15 on the L298 are connected to two 1/ 2- oh m power resi stors connected to ground. All drive currents used by the step- per 's t wo fi eld w ind ings are passed t hro ugh th ese resi sto rs. The resistor conn ected to pin I takes the cur rent fr om one of th e two field windings, w hile the pi n 15 takes t he curre nt fr om the othe r f ield win ding. These two resisto rs give the contro lling 1.297 a method of measuring t he c urre nt being induced wit hin the

18

Chapter 2 / Electronics

moto r. Th e L 297 measures t he voltage drop across these res istors to control t he PWM chopper ci rcu it used to control th e current w ithin the w indings of the ste ppe r motor. The 2 .2 K and 1 0 K resis- tor s connect ed to pin 15 (Vref) on t he L297 are used to set up a voltage divider. T he resu lt ing vo ltage appli ed to t he Vref p in is us ed a s a se t point again st th e measured vo ltage coming from t he field wind ings. When th e set po int is reached , th e power driv e stage within the L298 dri ving tha t winding is turned off, allowing the FR30 4 diodes to discharge th e field winding. The field wind ing sta ys off until the internal oscillator w ithin th e L2 97 times out and turns the field w inding back on . The 22 K resi stor and th e 3.3 nF capacitor co nnec ted

pin 16 on the L297 set up the timer 's cho p- per rate. C2, C3, an d C4 filter the power supply for the ele ct roni cs and motors. jP I pro vides power and gro und for th e circuit and the motors. jP2 is jumped to include the ci rcuit connected to p in I w ith pin 16 on the L297 on only one board of the th ree used ; th e other two have pin 16 on the L 29 7 jumped to gro und. JP3 pin I acc epts step signal s; pin 2 a ccepts dire ction sig na ls; pin 3 is use d to con- ne ct a ll dri ve r boards th at need to be sy nc ed and pin 4 is gro und . jP4 is s et to bring pin 19 on th e L297 high at pin 1 to provide full step motor drive or low at pin 3 for half step. JPS is set to brin g pin li on t he L297 high at pin I to use pha se driving or low at pin 3 to inhibit driv e.

Don 't wo rry to o much about und er standing how t his circuit wor ks;

as long a s yo u follow th e dir ection s closely, th e boa rd yo u build w ill function pr operly.

The Interface Board

This board is rea lly onl y a gateway that allows the com puter

send and recei ve signals to the driver s and limit sw itches. There isn 't mu ch to it a s ide from a co nnecto r for th e straight-through parallel port ca ble and so me co nnect io ns for the w ires coming from each of the dri ver boards and limit switches. If yo u refer to the sche ma tic (Fig ure 2.7) yo u w ill see wh y th e parts list is short.

19

,

l - - - -

CNC Roboti cs

RI R2_'\', R4_RS_R6_R7_~8,R9_

,,!;J.'!

' I

2

Figure 2 .7

Interface schematic.

20

~₁ 2 3 4 5 6 7 8 9 10 II 12 13 ----E 14

~ 16 _

4

t ~ ~ ~

Pin10 Pin 11 Pin12 Pin13

~V

P;n2-gmd

Chapter 2 / Electronics

Part Quantit y Desc ription T able 2.2

Conn 1 Rl-17 JPl-5

1 17

1-17 pin, 5-2 pin

DB 25 connector 4.7K ohm resistor Header material

InterfaceComponents

List

Th e 4.7 K resi stors limit cu rren t to protect the circuit and the par- all el port. Better methods of protecting the parallel port are to use an optical isolation circuit or install a parallel port card specifical- ly to be used w it h the interface; the cards are cheap insurance against damaging a motherboard . I bought a used computer sole- ly for u se with these boards becau se if I destroy it I wo n 't lose y ears of accumulated file s.

The pin out of th e interface board is straightforward. Pins 1-17 on jP 1 are conn ected to pins 1-1 7 of the parallel port of y our comput- er. jP2 is conn ected to pin 10 on jP I at pin 1 and to ground at pin 2.

jP3 is conn ected to pin lion jPl at pin 1 and to ground at pin 2. jP4 is conn ected to pin 12 on [P 1 and to ground at pin 2. jP5 is con- nected to pin 13 on IP I and pin 2 is connected to ground. I b rought pin s 10, II , 12, and 13 on JP lout to separate conn ectors to make hooking them to limit sw itches a little easier. At JP6, pin I is to be connected to 5 volts and pin 2 to ground on the pow er suppl y.

Thi s chapter w ill have given you an und erstanding of t he circuits that are needed to connect and control the stepper m otors with a comp ut er. You w ill al so ha ve become familiar with th e integrated circuits that the drivers are built around. This understanding will enabl e you to bett er troubleshoot your boards when they are com - plete. The next chapter deals w ith making the p rinted circ uit board s using the toner transfer method.

21

I

l - - - - - - -

CNC Robotics

L297 L297D

STEPPER MOTOR CO NTROLLERS

ORDERINGNUMBERS:L297 (OIP20) L2970 (5020)

• NORMALIWAWEDRIVE

• HALF/FULLSTEP MODES

• CLOCKWISEJANTICLOCKWISEDIRECTION

• SWITC HMODE LOAD CURRENT REGULA- TION

• PROG RAMMABLE LOA DCURRENT

• FEWEXTERNALCOMPONE NTS

• RESETINPUT&HOMEOUT PUT

• ENABL E INPUT

OlP20

• _~ ^{-- -}

5020

DESCRIPTION

Thel297/A/O StepperMotor ControllerIegener- atesfourphase drivesignals for

two

ABSOLUT EMAXIMUM RATINGS

feature of this device isthatitrequiresonly clock, direction and mode input signals.Since the phase are generatedinternallythe burden on themicro- processor.and the programmer,isgreatlyreduced.

Mounte d in DIP20 and8020packages,thel297 can be used withmonolithicbridgedrivessuch as theL298N or L293E,orwith discretetransistors and darlingtons.

Symbol Paramet er Value Unit

V. Supplyvoltage 10 V

V; Input signals 7 V

P~ Total powerdissipation(T"mt> - 70"C)

,

TItg.T_i Storage andjunct ion temp erature -40 to+ 150 "C

TWOPHASE BIPOLA RSTEPPERMOTORCONTROL CIRCUIT

••

_FlJtll" I e

!."OO...^Ie ll91 , 0

22

August1996 1/11

r- - - - - - - - - - - - - - - - - - - - - - -

Chapter 2 / Ele ctroni cs

L297-1.297D

PINCONNECTION (Top view)

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L297

1297D

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23

CNC Roboti cs

L297·l297 D

PINFUNCTIONS-l2971L297D

N' NAME FUNCTION

1 SYNC ^OUtputoftheon-chipchopper oscillator.

TheSYNCconnec tionsThe SYNC co-oecncos01alll297sto be sy nchrooi z ed arecoonecled togethe rand the oscillator components areomitted onallbutone.Ifan externalcloc k source is useditis inje ctedat thiste rmina l.

2 OND Groundconnec tion.

3 HOME Opencollec toroutpu tthat indicateswhenthe l297 is initsinitial slate(ABeD=0101).

Thetransistor isopen when thissigna l is active.

4 A Motor pha seAdrivesignalforpower stage.

5 INHl Activelow inhibitcontrolfordriver stageof A and B phases.

Whe na bipolarbridge is usedthis signalcan beused10 ensure fas!decay ofloadcu rrent when awindi ng isde-energi zed .Also usedbychopper10regulateloa d currentifCONT ROLinput is low.

6 B Motor phase8 driv e signa l for power stage.

7

e

S INH2 Activ elowinhibitcontrolfor drive stagesofC and 0 phases.

same function sasINH 1.

9 D Motor pha se0drive signal for power stage.

I .

11 CONT ROL Controlinp utthat delines actionofchopper.

When low chopperactsonINHl andIN H2;whenhighchopper actson phaselines ABC D.

12 V. 5V supplyinp ut.

13 SENS2 Input lorloa d cu rrentsensevo ltagefrompowerstages01pha ses CandD.

14 SENS, Input lorloa d curre ntsensevoltage from powerstages01phases AandB.

15 V., Referenc evoltagelor choppercircui t. Avolage applied tothis pin determinesthepeak load current.

AnRC network(Ato Vee.C to ground) comected to this terminal

, . ose

on allbutonedevice in synchronizedmulti -l297 config urations.I

==1I0.69RC

17 CWIC CW Clockwiseicountef'Clod(wisedirectioncontrolinpul.

Phy sical direction01motorrotation alsodepends onconnec tion ofwindings.

Sy nchronizedinte ma lly therefore directioncan becha nged at any time.

18 CLOC K Stepcloc k.Anactive low pulseon thisinput advancesIhe moto r oneinc reme nt.The step occurson the ris ing edge01thissignal.

--- liii SGS.~ ...::c.:.3/11

24

I

Chapter 2 I El ectron ics

1297· 12970

PINFUNCTIO NS . l2971L297 D(conlinued)

N' NAME FUNCTION

,.

Two-phase-onlullstepmode is set by selecting FULLwhe n the translatoris atanoddnumb eredposition.(The home positionis designate state 1).

20 RESET ResetinputAn activelowpulse on this inp ut restoresthe

translator to thehome position(state1,ABeD=010 1).

THERMAL DATA

Thermal resistance junction-ambient

Symb04 Parameter DIP20

max 80

SOlO Unit 100

o em

CIRCUIT OPERATION

TheLZ97isintendedfor use with a dualbridge driver, quad darlington arrayor discretepower devicesinstep motordrivingapplications. Itre- ceivesstepclock,directionand modesignalsfrom the systemscontrolle r(usuallya microcomputer chip)andgenerates control signals forthepower stage.

The principalfunctionsareatranslator,whichgen- erates the moto rphase sequenc es,anda dual PWMchoppe rcircuit which regulates thecurrentin themotor windings.Thetranslatorgenerates t hree differentseq uences,selectedby theHALF/FULL input.These arenormal(two phasesenergised ), wave drive(one phase energised) and half-step (alternatelyonephase energised/twophases en- ergised).Twoinh ibit sig nalsarealsogeneratedby the l297 inhalfstep and wave drive modes.These signals, whichconnect direct lytotheL29 8's enabl e input s,areintended to speed currentdeca y when a windingisde-energised.WhentheL297isused to drive aunipolar motor the chopper acts on these lines.

An inputcalledCONTROLdeterm ineswhethe r the chopperwill acton thephaselines ABCDor the inhibit lines INH1 andINH2.When the phase lines

4111

are choppedthenon-activephase line of eachpa ir (ABorCD) is activated(ratherthaninte rrupting the line thenactive).InL297+L298 configurationsthis technique reducesdissipationin the loadcurrent senseresistors.

Acommonon-chiposcillatordrivesthe dual chop- per.ltsupp liespulses at the choppe r rate whichset thetwo flip-flo psFF1and FF2. Whenthecurrentin awindingreach estheprogrammedpeakvalue the volta ge across the sense resistor (co nnected to one ofthese nseinputs SENSl orSEN&?) equals Vral and the correspo ndi ngcomparato rres ets its flipflop,inter rupting thedrive current until thenext oscillatorpulse arrives.The pea kcurrentforboth windingsisprogrammedby a voltaged ivideronthe V,alinp ut.

Groundnoise problemsin multip le configuratio ns canbeavoidedbysynchronising the chopperos- cillators. Thisis doneby connect ing allthe SYNC pinstogether.mounting the oscillatorRC network on one deviceonlyand groundingtheOSCpin on all other devices .

25

CNC Robotics

L297·l297D

MOTORDRIVINGPHASESEQUENCES The L29Ts translator generatesphase sequences for normaldrive,wave driveand half stepmodes.

The statesequences and output waveforms for these three modes are shown below. In all cases the translatoradvances on the lowto high transis- tionof~.

Clockwise rotationis indicate;for anticlockwisero- tation the sequences are simply reversed

liESET

restores the translator to state 1,whereABeD = 0101.

HALFSTEP MODE

Half stepmodeis selected by a highlevelon the HALFiFOITinput.

o

- ---,u r----,ur - -u - -

NORMAL DRIVE MODE

Normaldrivemode (also called"two-phase -on"drive)is selectedbya low level on the HALFJro[[ input when the translator is at an odd numberedstate(1,3, 5 or 7). In thismode the

mm

1001

€J~I010

[iJ 0 \ ,

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O IOI~ 0

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26

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Chapte r 2 / E lectronics

L297- 1297D

MOTOR DRIVINGPHASESEQUENCES(continued)

WAVEDRIVEMODE

Wavedrive mode (alsocalled"one-phase-on"drive)is selectedbyalowlevel ontheHALF/F'O[[ input whenthetranslatoris ataneven numberedstate(2,4,6 or 8).

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ELECTRICALCHARACTERISTICS(Refertothe block diagram Tamb=25"C,Vs=5Vunless otherwise specified)

Sym bol Param eter Testcond ltl o ns Min. Typ Max. Unit

V, Sup ply voltage (pin 12) 4.75 7 V

"

Quiesc ent supplycurrent (pin12) Outputs floating 50 BO mA

V, Input voltage low 0.6 V

(pin11,17,18, 19 , 20)

High 2 V, V

"

V~ Ena bl einputvoltage(pin 10j low 1.3 V

High 2 V, V

~, Ena ble inputcurren t(pin10) V....'"L 100 pA

V_en",H 10 pA

v;

=

(pins4,6,7,9)

10

=

V,nll Inhibit output voltage(pins5,8) 10 =10mA ViM L OA V

10= SmA Vir>h H 3.9 V

VSYNC Sync OutputVoltage 10=SmA VSYNCH 3.3 V

10=5 mA VSYNCv O.B

6111

27

CNC Robotics

ELECTRiCAL CHARACTERISTICS(continued)

L297·l297D

Symbol Pa ran eter TestcondItion s Min. Typ Max:. UnIt

I~. Leakage current(pin 3) VeE

=

V~ saturationvoltage(pin3) I ",SmA 0.' V

V~ Comparators offsetvoltage V,.,=.1V

s

(pins 13,14,15)

~ Comparatorbias current ·100 '0 pA

(pins13,14.15)

V~ Input refe rerx:evolage(pin 15) 0 3 V

teu< ^Clocktime 0.' us

ts ^{Setuptime 1 us}

IH ^Holdtime

•

'"

!RclK ^Reset10dockdelay 1 ps

Figure 1.

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28

_ _ _ _ _ _ _ _ _ _ I.jj

Chapte r 2 I El ect ronics

L297-L297D

APPLICATIONINFORMATION

TWO PHASEBIPOLAR STEPPERMOTORCONTROLCIRCUrr

This circuitdrives bipolarsteppermotorswithwindingcurrentsup to2A.Thediodesare fast 2Atypes.

1151RS1. ~O!in 01tvoa~Zot.~A ST0100£5

Figure3:SynchronisingL297s

1"- - -10

.~~ NSEI . SENS{; l

L298H

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WINDINGS

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L297 L297

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29

CNC Robot ics

L297-1297D

D1P20 PACKAGEMECHANICALDATA

mm Inch

DIM.

MIN. TYP. MAX. MIN. TYP. MAX.

at 0.254 0.010

B 1.39 1.65 0.055 0.065

b 0.45 0.0 18

b1 0.25 0.010

0 25.4 1.000

E 8.5 0.335

e 2.54 0.100

ea

F- 7.1 0.280

I 3.93 0.155

L 3.3 0.130

Z 1.34 0.053

,...

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B ....!...

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Z

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1 r

b1 E

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30

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L297-L297D

5020 PACKAGE MECHA NICAL DATA

Chapter 2 / Electronics

mm Inch

DIM.

MIN. TYP. MAX. MIN. TYP. MAX.

A 2.65 0.104

a1 0.1 0.3 0.004 0.012

a2 2.45 0.096

b 0.35 0.49 0.014 0.019

b1 0.23 0.3 2 0.009 0.013

C 0.5 0.020

ct 45(typ.)

D 12 .6 13.0 0.496 0.51 2

E 10 10.65 0.394 0.419

,

,3 11.43 0.450

F 7.4 7.6 0.291 0.299

L 0.5 1.27 0.0 20 0.050

M 0.75 0.030

S 8(max. )

D

M

10/11

31

G NG Robot ics

L297-L297D

Informationfurnishedis beneveo to be accurateand reliable.However,SGS-THOMSON Microelectronicsassumesno respons ibilitylor the consequences of useof such informationnor for any infring ementof patentsor other rights ofthird parties Which may resultfrom~suse. No license is granted byimplication or otherwiseunder any patentorpatentrights of SG5- THOMSONMicroelectronics.Specificationmentioned in thispublication are subject10 change without notice. This publication supersedes and replacesallinformation previouslysupplied.

SGS·THOMSONMicroelectronicsproducts are not authorizedfor use as critical compooontsinurescocort oevcasorsystemswithoutexpress wratenaporovaof SGS-THOMSONMicroelectronics.

"1996 SGS-THOMSONMicroelectronics-Printedin Italy-AllRights Reserved

SGS·THOMSONMicroelectronics GROUP OF COMPANIES

Auslralia - Brazil-Canada - China-France - Germany -HongKong· Italy-Japan -Korea- Malaysia- Mejta-Wtorocco-The Netherlands - Sinqapora . Spain-swsoen-Switzerland·Taiwan-Thailand•Un~edKingdorn ·U.S,A.

32

---LW ~

1- - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Chapter 2 I E lectronics

L298

DUAL FULL-BRIDGE DRIVER

.OPERATINGSUPPLYVOLTAGEUPT0 46 V

• TOTAL DC CURRENT UP TO 4 A

• LOW SATURATiONVOLTAGE

• OVERTE MPERATUREPROTECTION

• LOGICAL "0" INPUTVOLTAGE UPTO1.5 V (HIG H NOISE IMMUNITY)

DE SCRIPTION

Multlwatt1 5

'ili.

"'~

^.

TheL29g is an integrated monolithiccircuitin a 15- lead Multiwattand PowerS020packages.It is a high voltage, highcurrentdual full-bridgedriverde- signed to accept standardTTL logic levels and drive inductive loads suchasrelays,solenoids,DC and steppingmotors.Too enableInputs are provided to enableor disable the deviceindependentlyofthein- put signals. The emitters of the lower transistorsof each bridgeare connectedtogetherandthe corte - spondingexternal terminalcan be used for the con-

PRDE RI NGNUMB ERS: L29 SN (Multiwa tt Vert. ) l298HN (Multi watt Honz) L29 8P(Po we rS020j

nectionofan externalsensing resistor.Anadditional supplyinput is providedso that the logicworks at a lower voltage.

BL O C K DIA GRAM

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CNC Robotics

L29 8

ABSOLUTE MAXIMUMRATINGS

Symbol Parameter Val ue Unit

V, Powe r Supply 50 V

V", Logic SupplyVollage 7 V

V"V^{ert Input andEna bleVoltage}

-o.a to

'0

-NonRepetitive(I=lOQJJ.s) 3 A

-RepeUive(80% 011-20%otf;ton

=

--DCOperaticn 2 A

V_ SensingVoltage ~1t02.3 V

P", Total PowerDissipakn(Tease_75'C ) 25 W

T" Junc tbn OperatingTemp erature -25to130

-c

" c

"

Multl watt 15

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ra

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ro

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L

CURRENTseNSINGB

" " ' ' ' ' ' ' 4

ccrsur3 INPUT4 ENABLE 8 l~lPUT:I

LOGICSUPPLYVOLTAGE\Iss G'D

INPUT 1 ENABLE A INPUT 1 SUPP LYVOLTAG Elis OUTPUT2 OUTPUT1 CURRENTSENSINGA

34

GNO 20 GND

"~ A 19 "~6

NC.

te

D,," 4 17

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V, 6 15

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THERMALDATA

Symbol Parameter PowerS020 Mu ltlwatt 15 Unit

Rt,,1"CMe ^ThermalResistalce Junctiarcase Max. - 3 'CNi

R,.,i-tlmb Thermal Resistanc e Junctioo-ambiEl'l1 Max. 13 n 35 ^<C/W

(")Mourledoo alumirumsubstrale 2/13

Chapte r 2 / E lect ronics

L298

PINFUNCTIONS(refer totheblockdiagram)

MW.15 Pow erSO Name Function

1;15 2;19 SenseA:SenseB Between this pinandgrou njis connected the sensereestorto contra the currertof theload

2;3 4;5 Out1;Oul2 Outputs althaBrid ge A;the current that flows through theload connected between these two pinsis monitored at pin 1.

4 6 Vs SupplyVoltage for the Power OutputStages.

A I'lOIl-indu:tive 100nFcapacik:lrmust be oonnecled between this pin and groll"ld.

5;7 7:9 Inp ut 1;Inp uI 2 TTL

comoauae

6;1 1 8;14 Enable A;Ena ble B TTL Compa'bleEnableInput thel stale disablesthe bridge A (enaJj eA)ancVor the bri:lgeB(enableB).

•

9 12 VSS SUpp¥ Voltagefor thelog icBlocks.A1oarr capacior must be conneded between this pinand ground

10:12 13;15 Inpul3:Input4 TIL Comoatiblelooutsofthe Bridge 8.

13;14 16;17 OUI3;OuI4 Outputs 01the Bridge8.The currere that flows Ihroughtheloa::l connected between these two pinsis mooitoredat pin15.

-

ELECTRICA L CHARACTE RISTICS(Vs

=

=

=

Symbol Parameter Test Conditions Min. Typ. Max. Un it

V, SupplyVoltage(pin 4) Operativeccnonco V,to!+2.5 46 V

Vss Logic Supply Voltag e (pin9) 45 5 7 V

I, Oulescerr Sup ply Current(pin4) VQn _H; <_0 V; _L 13 22 mA

VI= H 50 70 mA

Van= L V,=X 4 mA

Iss ^Quiescert Curre ntfromVss(pin 9) Ven- H: IL-0 V

i_L 24 36 mA

VI=H 7 12 mA

Yen=L V,=X 6 mA

V,L InputLow Voltage -0.3 1.5 V

(pins5.7,10, 12 )

V" Input HighVo ltage 2.3 VSS V

(pins5.7, 10. 12)

"

""

(pinsS.7. 10.12)

I. High Voltage Input Current Vi = HsVss--o.6V 30 100 "A

(pinsS,7,10,12)

V",, _L Enablelow Voltage(pins 6, 11) -0.3 1.5 V

V.... =H Enable High Voltage (pins6.11) 2.3 V" V

len_ l low VoltageEnableCurrent Veo-l 10

""

(pins6,1 1)

I,."_H HighVoltageEnable Current Ven-Hs

v se

VCEsaHH) SourceSaturation Voltage IL- 1A 0.95 1.35 1.7 V

IL=2A 2 2.7 V

VCENI(l ) SinkSaturation Voltage 1t.-1A (5) O.BS 1.2 1.6 V

IL-2A (5) 1.7 2.3 V

VeE,.. To talDrop 1t.-1A (5) 1.80 3.2 V

IL-2A (5) 49 V

V_ SensingVol tage(pins1,15) -1 (1) 2 V

3113

35

- - -- - - - -- - - - -