Reading time ( words)
In the June 2020 issue of Design007 Magazine, the I-Connect007 editorial team interviewed design instructors Rick Hartley and Dan Beeker regarding their belief that designers should not trust app notes until they've been proven to be accurate. After the issue was published this week, Rick emailed us with a few more points that he wished to contribute to the ongoing app note conversation.
After reading the June issue of Design007 Magazine on app notes, I realized there is one key point that I have not pushed hard enough. My real heartburn, and Lee Ritchey’s and Dan Beeker’s for that matter, is that app notes are mostly insufficient in the area of PCB design guidance—not in the area of circuit design assistance and advice.
Back in the days when PCB design was “Who cares?” app engineers were the circuit design engineer’s best friend. But in these days where PCB design really matters, they frequently fall on their face, since colleges teach nothing about PCB design for SI and EMC.
This really came home to me when I read the interview with Geof Lipman. Barry Matties stated to Geof, “We see some of the industry’s top design instructors telling their classes, ‘Don’t trust app notes. Assume they are wrong until proven right.’” Geof reacted, “They might have been being dramatic. I’m not sure.”
I can tell you with absolute clarity that neither Lee, Dan, nor I are being dramatic. The problem is that the information that Geof gleans from app notes is much different than the info PCB designers take from them. Simply put, app engineers do not understand how PCBs work. They think they do, but they do not!
There are, however, a couple of exceptions to the premise that most of the problems with app notes have to do with PCB layout. One of these is something that Dan Beeker pointed out in the interview: the fact that many app engineers seem to be in love with the idea of putting ferrites on the power pins of digital ICs. That’s one of Lee’s pet peeves also. He even discusses this in the second volume of his book Right the First Time.
Thanks for allowing me to clarify.