Linear Technology’s Chief Technology Officer Robert Dobkin has been contributing Ideas for Design (IFDs) since his youth. He’s still enthusiastic about them. “I remember one I wrote when I was a kid. It was a current source that you could pulse on or off. I don’t know how many letters I got from that,” he said.
“It had just two or three transistors in it, but it was really effective in terms of people coming back to me after reading it, which means there were a lot of people out there who couldn’t do that,” he added. “Also, of course, it was useful. There weren’t many couple-transistor circuits that provided a current source you could turn on and off.”
Dobkin breaks down IFD articles functionally into those that provide a basic framework for inexperienced designers to follow and those that go beyond some component’s intended function to provide a novel solution.
With respect to the former, he says, “I think those IFDs are one of the best parts of the magazine—parts that get torn out and stuffed in peoples’ drawers. They’re important because if you look at the population of engineers, most of them, when they first came out of college, they can look at a circuit, they can understand it, they can modify it, but they can’t really design it from scratch.
“So all these guys ought to want to collect ideas for circuits that do something, and now they’ve got some seeds to start from. So sometimes the IFD gives a starting point for a lot of different kinds of solutions... and hopefully it was done by somebody who really knew what he was doing so it really works when it gets put together.
“Or they’re digital engineers,” he mused. “They can do this complex digital thing, but if they try to put three or four transistors together, that’s not what they’re trained to do. So IFDs provide a nice way of getting solutions to these people, too.”
The second kind of IFD, Dobkin says, “is one that provides kind of a neat solution. Somebody came up with a way to use an IC ‘off-application.’ They found out that the ‘XYZ’ pin will also do something undocumented if you feed a signal into it. So they wrote a little IFD about that.”
Building Blocks Along those lines, I asked Dobkin about IFDs that take advantage of some non-ideal characteristic of the part, for example, when a transfer characteristic exhibits negative resistance. He said those IFDs generally originate with the applications engineering department at the manufacturer.“That’s because most customers can’t get inside the part. There isn’t enough information in datasheets nowadays to allow customers to get inside the part and use it off-application,” he said. “At one time, all datasheets included the actual circuit diagrams. That doesn’t happen now. So, you can’t tell exactly what’s going to happen on the pin without that.”
Since Linear is best known for basic “building block” parts, I asked whether they lent themselves more to IFDs than more application-focused parts. “I hope so. We try to come out with generalpurpose parts that people will use for years. Even the new ‘3080’ is one of those. (The LT3080 LDO is a descendant of the classic LM317. Dobkin was directly involved in designing both. See the figure.)
That’ll still be in use years from now,” Dobkin said. “As a building block, it’s not an end in itself all the time. A power-supply circuit can be used as an amplifier. It can be used as an isolator. It can be used as many things besides just a power supply. It can be used as a power control. It can be used as a battery charger. You don’t have to put too much around it to change its overall function,” he said.
Getting back to IFDs and educating recent engineering grads, I mentioned that ED receives many IFD contributions from universities around the world. As someone involved in hiring designers worldwide, did he perceive any differences in the way universities teach young engineers these days that affect their approach to basic components? For the sake of talking about that basic design instinct, he chose to address the engineers who come from countries that were formerly behind the Iron Curtain.
“Those engineers, those students, they didn’t have access to a lot of common ICs, so they used to build things out of transistors, which they could get,” he said. “So you’ll see more transistor-level designs coming out of there because the engineers have more hands-on experience with bipolar discretes that we get here. I think all engineers should have some experience designing at that level.”
Finally, I had to ask him what he didn’t like about IFDs. “The thing I dislike most are the IFDs that don’t work. The contributor hasn’t thought it through, hasn’t built it, doesn’t understand or doesn’t talk about the potential problems. It’s not hard to come up with an IFD and put it on a piece of paper, but if you haven’t built it, you don’t know about all its problems. You need a capacitor here to make it work, the supply bypass leads have to be close by, details like that,” he said.
“That’s a difference between a magazine’s IFDs and a company’s app notes. If somebody takes a reference design out of one of our app notes and it doesn’t work, he knows who to call. If he gets an idea out of a magazine and it doesn’t work, he should at least have the e-mail address of the author.”