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Linear's chief architect on power loss, IC design

Posted: 16 Jul 2007 ?? ?Print Version ?Bookmark and Share

Keywords:analog ICs? efficiency vs. power loss in IC design? IC design issues?

Dobkin: Designing for ICs is like writing poetry. You have to know all the bits and pieces to make it work. It is fun, but it is hard work too.

Linear Technology Corp. has grown steadily throughout its entire 25 years. Its margins are about 40 percent, partly because the high-performance analog chipmaker moves quickly to pioneer new markets when prices in existing ones begin to commoditize. Linear is currently focusing on such emerging markets as PoE chips, which let Internet-based phones get power through the phone cable. In April, it announced an accelerated stock repurchase transaction to buy back $3 billion of its common stock!more than 30 percent of the Milpitas-based company's market capitalization. The typical analog chip company's market cap is 11 percent cash.

One source of Linear's success has been its co-founder and chief technical officer, Robert Dobkin, who has been involved in the development of high-performance linear ICs for more than 30 years and has generated many industry-standard circuits. In this interview with EE Times, "Dobby," as some colleagues call the sexagenarian, talked about his favorite topics!Linear itself, and larger design issues such as efficiency vs. power loss.

EE Times: Efficiency has been the buzzword lately!efficiency of computers and desktops for the server market and the telecom market. What's your take?
Robert Dobkin: Everybody talks about efficiency, but it's the wrong thing to discuss about. They need to talk about power loss. The two are related, but you focus on the wrong thing when you talk about efficiency.

Efficiency changes with the voltage, so it depends on what the output voltage is. Power loss is pretty much independent of that. Let's say I have a supply with 1V at 10A, and it's 80 percent efficient. If I change the output voltage to 2V, it's now 90 percent efficient, but it dissipates the same amount of power. Power loss is the same at 2W.

If you look at what's happening in a switching regulator, there's quiescent current, which is input-supply-related; there are switching losses, which are frequency- and input-supply-related; and there are IR losses!the resistance losses!that are output-current-related. There's no inherent relationship to output voltage. If you look at a bunch of switches on the different company datasheets, and you look at the power loss at the different output voltages, they are all the same.

From the engineer's standpoint, when you are designing these devices, power loss tells you how big your power is and what you think it's going to be. If you're running on a battery system, it tells you how much wasted power you have. Efficiency is a good number, but power loss is a more important number. So companies may talk about efficiency, but what they are really saying is that they have low power loss.

You deal with efficiency vs. power loss when you have a badly operating design. When you are on standby power, you still have memory to keep alive; you don't really care whether it's efficient or inefficient, you just want to know what the minimum power loss is at that point to keep the memory alive. So power loss tells you how long your battery life will be.

Efficiency is a function of output voltage, so if the manufacturer wants to make a switching regulator "good," he specifies it at a higher output voltage, and it's now more efficient. And if a competitor says the output voltage is adjustable between 1V and 4V, he will specify it at 3.3V because he will get a really good efficiency number. Someone who specifies it at 1.2V will get a worse number.

It's not wrong to talk about efficiency, but it doesn't give you the whole picture. So if we get a call from a customer and he says they are looking at our part but a competitor's part is five percent more efficient, they need to know that the competitor is specifying the output at 3.3V while we are specifying it at 1.2V.

Let's talk some about the direction of the company and the recent changes at the top.
As I'm sure you've noticed, Dave Bell left the company as president in January. I am still the CTO, but I'm now taking a more active role, helping to fill in along with CEO Lothar Maier.

Linear is a high-performance company, and when things shift to low performance and commodity, then we are getting out of that business.

Is there a connection between Bell's leaving and a change in market focus?
I think Dave's perception of where he wanted the company to go and where it was going weren't quite the same, and he wanted to do some other things. He left on very friendly terms.

What should power design engineers focus on?
Designers should focus on power loss and manufacturability. And depending on the system size, they may want to include monitoring, which is on the PMBus. I think the digital-power view is overhyped.

I remember when we started analog ASICs vs. digital ASICs. LSI Corp., formerly LSI Logic Corp. and VLSI Technology Inc. were going great guns with digital ASICs. There's a place for digital power, but the most important portion of it by far is the telemetry.

I don't think a customer cares if the system is analog or digital, as long as it works. In theory, digital can help you do some sophisticated things!you can change the frequency response as a function of load steps and change it back again. But is it going to be worth it? And what kind of problems will it generate?

If you have a well-controlled system that doesn't oscillate and then you start playing with it and you change the frequency response of the system, are you going to get certain kinds of loads that will make it oscillate for a few cycles, or settle down? You don't know. But if the digital system works and it's not too expensive, then the user doesn't care.

What's Linear's take on supporting digital power designs?
We will certainly support the telemetry sections, and that will probably be supported within switching regulators. But that's a development project, and we're looking at all the options. If it costs more to do functions digitally than in analog, we won't do it.

Are you looking at retiring anytime soon?
This is my life, and I like what I'm doing. It's a creative outlet. It's like learning a foreign language: You have this thing that you want to translate and you know the basics, and you look up the other pieces and start writing some equations to figure out what the things are doing. But all that knowledge has to be part of you.

And designing for ICs is like writing poetry. You have to know all the bits and pieces to make it work. It is fun, but it is hard work too. And when you design an IC, you have hundreds of thousands of people who know exactly who to call!remember the datasheet!if something goes wrong with that IC. Indeed, it is like writing poetry.

-Paul O'Shea
EE Times




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