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If you’re a PCB designer or design engineer, you’re probably familiar with app notes—documents produced by the chip makers and other suppliers that are supposed to provide design teams with vital information for creating better circuit boards. But do app notes do what they’re supposed to do?
There’s a disconnect in the design segment. Some designers say they follow app notes every time, but a growing number of designers approach app notes with a wary eye. Many of the leading voices in the design community have been advising designers not to rely on app notes without running the numbers first. We decided to ask PCB design instructors Rick Hartley and Dan Beeker to help us shine a light on this issue.
Andy Shaughnessy: A couple of years ago, while Rick was doing a class, somebody in the class stood up and said, “We’re required to follow the app notes.” Rick, you almost had a heart attack.
Rick Hartley: I start all my classes with a comment I heard Lee Ritchey make 27 or 28 years ago, that app notes produced by IC manufacturers should be assumed wrong until proven right. A few people questioned him and said, “They’re not all wrong.” Lee responded, “I didn’t say that. I’m telling you that enough of them are wrong that you should not assume they’re right; you should assume the other way and prove they’re right if you believe they are.”
When Lee made the statement, I giggled, and he asked, “Do you disagree with me?” I said, “No. I’ve believed that for some time, and I’m glad to see there are two of us.” And then we both laughed. Dan Beeker is the one who made me understand. I had always had heartburn with app notes, but I never thought about why until I attended one of his classes. Somebody asked Dan, “What’s wrong with them?” because he made a similar comment in the class that app notes aren’t always good advice. He said, “App engineers all understand circuit theory. They all have a circuit background and can talk about schematics all day long, and they’re right 99% of the time. What they don’t understand is PCB layout.” Would you like to comment on that, Dan?
Dan Beeker: Yes. These guys have the greatest intentions. But even if they’ve been involved with board layout, it’s for a test board or evaluation board. If they are going to sell it, the highest level of certification is at the commercial level. Typically, they are not involved at that point. A team does the CAD work, and that’s the way the board comes out. If anything, they start with an app note that somebody else had written in the past that’s sort of close to what they need. And this is not their primary job; this is the second, third, or tenth job on their list, but they get hammered if they don’t write app notes, so they take one that exists. They do their best to copy and edit it so that it matches the product or application that they’re working on, and then that goes out the door. There’s not a lot of detailed peer review because if you’ve been in those types of design reviews, everybody sits in a room, you don’t look at it until you get there, and then you all agree that it’s a good thing and go out the door. The app note goes out.
To read this entire interview, which appeared in the June 2020 issue of Design007 Magazine, click here.