Issue link: https://iconnect007.uberflip.com/i/1256432
14 DESIGN007 MAGAZINE I JUNE 2020 Even to the level where I was engaged in a corporate-level evaluation team, we went through all the app notes that we could and looked for the ones that were probably okay, not very good, and were dangerous, and we made the lists and presented it to our corpo- rate marketing people. Their response was that they would rather have bad app notes than no app notes, and they wouldn't take even the ones that were blatantly incorrect off of the website or from the information sources. I've been involved in that too. I was one of those circuit guys who did a few ap- plication notes, and I was all smiles without a clue about what was going to end up hap- pening. Hartley: About a year ago, I was at a compa- ny doing some training, and a guy brought me an app note and said, "Based on what you've said in the first day and a half, I get the feeling this app note is way out in left field." It had a feedback line in a switch-mode power supply where they had suggested isolating the ground for it away from the other grounds. I'm sure Dan's cringing right now because it's problem number one. On top of that, with the exam- ple they showed in the app note, they split up the ground signal and its return. At least you have to put them together to contain the fields. Then, they routed the trace and feedback line with a different ground. I see stuff like this all the time. Beeker: And you'll see it on datasheets where there will be an analog and a digital ground, especially on voltage regulators. When I con- fronted the IC designers, they admitted that it's there for test, and they didn't expect people to see that. Even in their own design, there are control signals that go from the digital side to the analog side that depend on the two grounds being connected at the PCB. Otherwise, even in their control of the switching power supply, the control signals would then have to go find the magic isolation point, whether that was a star connection, inductor, or a ferrite, which people love for some reason. Then, they play back to the die. 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 eval- uation board. If they are going to sell it, the highest level of certification is at the commer- cial 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 any- thing, they start with an app note that some- body 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 ex- ists. 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. Rick Hartley