pease, r. a. (1991) troubleshooting analog circuits

ROBERT A PEASE Tr o u b I e s h o o t I n a Analoi Troubleshooting Analog Circuits National El Semiconductor Troubleshooting Analog Circuits With Electronics Workbench Circuits Robert A. Pease and Interactive huge Technologies Newnes Boston Oxford Johannesburg Melbourne New Delhi Singapore Newnes is an imprint of Butterworth-Heinemann Copyright @ 1991 by Butterworth-Heinemann Paperback reprint 1993. A member of the Reed Elsevier group All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic. mechanical, photocopying, recording. or otherwise, without the prior written permission of the publisher. Recognizing the importance of preserving what has been written, Butterworth-Heinemann prints its books on acid-free paper whenever possible. Butterworth-Heinemann supports the efforts of American Forests and the Global ReLeaf program in its campaign for the betterment of trees, forests, and our environment. ISBN 0-7506-9949-8 The publisher offers special discounts on bulk orders of this book. For information, please contact: Manager of Special Sales Butterworth-Heinemann 225 Wildwood Avenue Wobum, MA 01801-2041 Tel: 78 1-904-2500 Fa: 781-904-2620 For information on all Newnes publications available, contact our World Wide Web home page at: http://www.newnespress.com 20 19 18 17 16 15 14 Printed in the United States of America Contents Foreword vii Acknowledgments x About the Author xi I. First Things First: The Philosophy of Troubleshooting 2. Choosing the Right Equipment 3. Getting Down to the Component Level: Resistors and Inductors 26 4. Getting Down to the Component Level: Capacitor Problems 40 5. Preventing Material and Assembly Problems: PC Boards and Connectors, Relays and Switches 50 6. Understanding Diodes and Their Problems 65 7. Identifying and Avoiding Transistor Problems 77 8. Operational Amplifiers-The Supreme Activators 9. Quashing Spurious Oscillations 108 I 0. The Analog-Digital Boundary: A Never-Never Land? I I. Dealing with References and Regulators I 2. Roundup of “Floobydust”: Loose Ends That Don’t Fit Elsewhere I 3. Letters to Bob 155 I 4. Real Circuits and Real Problems 1 14 89 120 135 143 172 Appendixes A. Digital ICs with Nonstandard Pinouts B. Operational Amplifiers with Nonstandard Pinouts C. Understanding and Reducing Noise Voltage on Three-Terminal D. Testing Fast Comparators for Voltage Offset 194 E. VF VS. IF on Various Diodes F. How to Get the Right Information from a Datasheet G. More on SPICE 203 H. Pease’s Troubleshooting Articles as Originally Published in EDN 208 187 188 Regulators by Errol1 Dietz 191 196 199 Index 209 V Foreword “Your idea is so good that, if you give me 20 minutes, I’ll be sure that I was the first one to think of it.” Although I pass out that accolade sparingly, if I were to do what the compliment implies, I’d surely claim credit for the idea of publishing Bob Pease’s series on “Troubleshooting Analog Circuits” in EDN Magazine Edition. The fact is, though, that the idea came from Jon Titus, W, Editorial Director, and Chief Editor of EDN magazine and from Tarlton Fleming, then an EDN Associate Editor and now Manager of Applications Engineering at Maxim Integrated Products Corporation. (and Cahners Publishing Company’s) Newton, Massachusetts, headquarters were brainstorming ideas for articles we could solicit from contributors in industry. Jon ventured that because EDN readers always look to the magazine to provide practical ideas on how to do their jobs better, and because trouble is ubiquitous, articles on how to troubleshoot more effectively should be a natural for us. regular basis, as Bob reviews the analog design ideas submitted by EDN readers. Tarlton recalled Bob’s mentioning a book he and his colleagues at National Semiconductor were planning to write on power-supply design. Tarlton said he thought Bob had already put together some material on troubleshooting. We needed to find out whether National would grant EDN the rights to publish a portion of the book. Tarlton would open the discussions. of what would eventually become the first three installments of Bob’s series. By then, Tarlton had left the East Coast to seek fame and fortune in Silicon Valley, so the task of reviewing Bob’s material fell to me. I skimmed through it quickly and became quite intrigued. I am a contemporary of Bob’s; actually, I am a few years older. Though we did not know each other at the time, I was a graduate student in EE at MIT while Bob was an undergraduate there. I first became aware of Bob when he was working for his previous employer, George A. Philbrick Researches, now a part of Teledyne Components in Dedham, Massachusetts. Even in those days-the sixties and early seventies-Bob was a prolific writer. He shared his musings and technical insights with Philbrick customers and other analog engineers who read the firm’s house organ, “The Lightning Empiricist,” and with readers of trade magazines, such as EDN. Those earlier writings did a lot to burnish Bob’s image as a technical expert, but they had a secondary effect as well: They made his sense of humor and his passion for puns something of a legend. As a form of humor, plays on words are denigrated by all too many people. However, at least a few openly admit to enjoying puns, and that pup includes Bob and myself. Many years ago, when I first read material Bob had written, I suspected that if I ever met him, I’d probably like him. When I started to read what he had just submitted to EDN, the experience was a bit like a chance encounter with an old friend after not meeting up with him for a long time. but it was lighter than most of what we publish. There were few equations and no In early 1988, Jon and those EDN technical editors who work at the publication’s Tarlton, who edited EDN’s popular Design Ideas section, worked with Bob on a Shortly afterward, a good-sized package arrived at EDN’s offices. In it was the text The material was somewhat out of the ordinary for EDN. It was technical, yes . . . vii viii Fw+word complex schematics. Would the readers like it? My guess was they would; the manuscript was filled with pithy and trenchant observations. The style was different too. In the past, rigid constraints forced articles into a ho- mogenized mold-albeit one that, despite the magazine’s highly technical content, was almost always eminently clear and readable. Now we’re a bit more relaxed. We still rewrite extensively for clarity, but we try to let a writer’s style and personality show through. I think part of the reason for our change in attitude was the success of Bob’s series. Bob’s style not only displays his sense of humor, it showcases his idiosyncratic and sometimes quirky nature. Most of all, however, his perfectionism and consum- mate craftsmanship are clearly evident. I pointed out that if we tried to force what Bob had given us into a more traditional mold, it would lose a significant part of its value. Among the reasons that Bob is so successful are who he is and how he ap- proaches problems. There was no better way than through his style to convey the essence of Bob’s personality to the readers. One of EDN’s “rules” is that we don’t use rhetorical questions; readers may an- swer them in unexpected ways-ways that can play havoc with the point the writer is trying to make. The staff jokes that we “ration” rhetorical questions. According to the legend, each issue, our managing editor, Joan Morrow Lynch, grants one editor who requests it the right to ask a rhetorical question. She does so on a first-come, first- served basis, but can only deny the privilege to anyone whose recent work has posed too many of the queries. After reading what eventually became the first installment of “Troubleshooting Analog Circuits,” I observed that this one article would more than use up EDN’s en& annual allotment of rhetorical questions. “But, why not risk it?” I asked; Bob begins solving problems by asking questions. Something about the series that, to my knowledge, is unique is that it approaches the subject of troubleshooting from a design engineer’s perspective. EDN readers are designers. Pease is an accomplished designer. Yet he is one who not only doesn’t see troubleshooting as beneath his exalted station, he views the activity as part and parcel of his job. Indeed, he revels in it, and his writing effectively communicates his pas- sion for exorcising the hobgoblins that bedevil electronic circuits. That fact was not wasted on the readers. Their reaction was overwhelmingly posi- tive. Never in the magazine’s history (almost 35 years) has something that EDN published evoked such an enthusiastic outpouring. Every few weeks, a new deck of reader-service cards circulates around our offices. There are the cards on which readers have written comments-in addition to making requests for more informa- tion on products advertised and mentioned in the magazine. The decks for the issues that contained the series installments invariably contained scores of hand-written notes asserting that Bob’s articles were marvelous; the best that EDN had ever printed. In fact, EDN’s readers voted all 12 articles the best-read contributed manu- scripts in their respective issues. Once the series ended, we started getting cards that asked for the articles in book foxm. First, the book requests were a trickle, but they rapidly swelled to a torrent. So, for all of you who asked for it and for those who never saw the series in EDN but who have decried the lack of a compendium on troubleshooting from a designer’s perspective, here it is. make it clear that I wasn’t even the one who did the most editing. In addition to my- self, the technical editors were Senior Editor Charles H. Small, and Anne Watson Swager, now EDN’s East-Coast regional Editor in Wynnewood, Pennsylvania. The nontechnical editing of every article in the series was done by Associate Editor Julie Anne Schofield. EDN’s Art Department, directed by Ken Racicot, handled the Lest it appear that I was the sole EDN staff member who edited Bob’s work, let me Foreword ix graphic work in Newton. In addition, many of the photos were taken by Bob’s col- leagues at National Semiconductor. Despite its length, this list of contributors isn’t complete. A magazine is the work of many people, and any list inevitably omits someone. What should be apparent from the above is that working on the series was fun! When he first interviewed me for this job at EDN, Roy Forsberg, now publisher of another Cahners magazine, Test and Measurement World, remarked that a technical editor’s job was the best job in all of electronics. At the time, I passed off Roy’s com- ment as somewhat self-serving. But working on the Pease series dispelled any doubt I might have had about how much fun the job can be. Working on the series was a great experience! As important as Bob’s tips on troubleshooting are, I hope the se- ries-and now the book-provide more; I hope they communicate the exhilaration felt by all of us who were involved with the project. Dan Strassberg Associate Editor EDN Magazine [...]... lot of other analog circuits and may even be useful for some basic digital hardware You don’t have to build switchers to find this book useful; if you design or build any analog circuits, this book is for you Maybe there are some engineers who are knowledgeable about digital circuits, computers, microprocessors,and software, who may someday write about the troubleshooting of those types of circuits That... to you if you try to slough off your troubleshooting chores we have all seen it happen If you have a bunch of analog circuits that you have to troubleshoot, well, why don’t you just look up the troubleshooting procedures in a book? The question is excellent, and the answer is very simple: Until now, almost nothing has been written about the troubleshooting of these circuits The best previous write-up... and suggestions on what to look for when troubleshooting data converter and analog circuits What’s missing, though, is general information When I started writing about this troubleshooting stuff, I realized there was a huge vacuum in this area So I have filled it up, and here we are You’ll probably use general-purposetest equipment What equipment can you buy for troubleshooting? I’ll cover that subject... years ago we had so many nagging little troubles with band-gap reference circuits at National, that I decided (unilaterally)to declare myself “Czar of Band Gaps.” The main rules were that all successful band-gap circuits should be registered with the Czar so that we could keep a log book of successful circuits; all unsuccessful circuits, their reasons for failure, and the fixes for the failures should... up a leaky PC board-r a leaky, dirty IC package When Computers Replace Troubleshooters, Look Our Now, let’s think-what needs troubleshooting? Circuits? Television receivers? Cars?* People? Surely doctors have a lot of troubleshooting to d e t h e y listen to 2 If you don’t think troubleshooting of cars can be entertaining, tune in Car Talk with Tom and Ray Magliozzi Ask your local National Public Radio... borrow all that equipment When is an analog voltmeter better than a DVM? Well, the analog voltmeter usually has inferior accuracy and resolution, but when you watch an ordinary analog voltmeter your eye can detect a trend or rate-of-change that may be hard to spot on a DVM, especially in the presence of noise or jitter As an example, if you suddenly connect an ordinary analog volt-ohmmeter across a 1 p,F... describing how the product is supposed to work, and the designer isn’t around any more If there’s ever a time when troubleshooting isn’t needed, it’s just a temporary miracle You might try to duck your troubleshooting for a while You might pretend that you can avoid the issue And, what if you decide that troubleshooting isn’t necessary? You may find that your first batch of products has only three or four failures,... that have stumped other engineers, and reviewing colleagues’designs In a similar vein, Bob is a long-time contributing editor who reviews design-idea submissions of analog circuits for EDN magazine I First Things First The Philosophy of Troubleshooting In this first chapter, I will make the point that a significant part of effective troubleshoDting lies in the way that you think about the problem The... only offers a few pages of troubleshooting advice, and there is much to explain beyond what he has written Another book that has several good pages about the philosophy of troubleshooting is by John I Smith (Ref 2) Smith explains some of the foibles of wishing you had designed a circuit correctly when you find that it doesn’t work “right.” Unfortunately, it’s out of print Analog Devices sells a Data... volunteered to write a chapter, and I volunteered to do a chapter on troubleshooting At present, the status of that book is pretty dubious But, the “troubleshootingchapter” is going strong, and you readers are among the first to benefit, because that one chapter has expanded to become this entire book Although I am probably not the world’s best analog- circuittroubleshooter, I am fairly good, and I just happened . possible errors, before the wafers were fabricated, and we’re gaining. In addition, we have added Czars for start-up circuits and for trim circuits, and a Czarina for data-sheet changes, and we are. Publications in San Diego. Each one really worked hard, and cared a lot about every word and phrase that we debated and argued and polished and refined. I am also grateful to Joyce Gilbert,. Butterworth-Heinemann Paperback reprint 1993. A member of the Reed Elsevier group All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted