Electronic Design

Letters

Multiphase PWM Controller ICs
I wish to go on the record regarding Linear Technology Corp. and its PolyPhase controllers. This multiphase type of PWM controller was the subject of the recent report, "Power-Supply ICs Go Multiphase To Take On 100-A Loads" \[March 4, p. 42\].

The leadership position of Linear Technology in multiphase controllers may not be well known to the broad marketplace. For example, in September of 1995, our patent artwork showed detailed schematics of how our LTC1436 phase-locked loop could be configured with an external clock to provide multiphase operation. Thus, we first demonstrated the viability of producing an integrated multiphase controller IC a full three years ahead of the first commercially available chip. Just as important, we pioneered the use of synchronous architectures for monolithic multiphase controller ICs with the introduction of our LTC1628 device to selected customers in December of 1998, and to the general market in May of 1999. This chip, like the rest of our PolyPhase family, includes its own MOSFET drivers, which considerably reduce the external component count. The resulting system benefits are smaller footprint, higher reliability, and lower cost.

The breadth of our PolyPhase products addresses numerous applications. We currently have over 20 different multiphase products in our portfolio, with another three to be introduced during the next couple of months. Our broad line includes controllers that provide single or dual outputs and deliver output currents of up to 60 A at output voltages as low as 0.6 V. Moreover, in addition to single-package 1-, 2-, or 3-phase monolithic controllers, we can provide 4-, 6-, 8-, 10-, and even 12-phase configurations that handle currents of 240 A at sub-1 V.

Tony Armstrong
Product Marketing Manager
Power Business Unit
Linear Technology Corp.

Design Of 50 Years Ago Versus Today
I disagree with two statements that you made in "Design Through The Decades" \[Jan. 7, p. 24\]:

  1. My parents bought an Admiral TV in 1950, so the government wasn't the only electronics customer. Engineers had to start thinking about cost when designing TV sets. Look at Earl Munzer.
  2. Today when I need +20 dB of gain, a simple op amp and two resistors does it. I usually don't worry about load impedance (as long as it isn't something extremely low). Fifty years ago, there would have been much design work with vacuum tubes, interactions of one stage loading another, and no calculator. Design wasn't always simpler.

Martin Risso
Omnitronics LLC

Author's Reply: You're partly correct in that the government wasn't the only customer. I wrote that "The government was the largest and often the only customer." There were manufacturers of consumer electronics items like TV sets and record players, but by and large, most of the industry's work targeted defense and aerospace, and the government was indeed the ultimate customer.

As for your second point, I incorrectly implied that design engineering was simple. Indeed, it was challenging because engineers then could only rely on their education to solve engineering problems. Engineering today is even more complex, even though a designer has a huge array of tools available to help. On the other hand, today's designers must deal with a larger, more complex system-level approach versus engineers of 50 years ago who only had to consider a much smaller part of a larger design problem. Thanks for helping to clarify my retrospective.

Roger Allan

Invest In The Future
I found your editorial on investing in infrastructure to be very interesting \["It's A New Year—With A Fresh Chance To Recover," Jan. 21, p. 18\]. I fully agree with you that an investment in the future must be made. Just look at some of our highways, sewers, and water systems, and you can see the result of not investing. But your last paragraph is what I'm writing about. I don't feel that the government should have any role in financing the infrastructure. Every time the government's tentacles are involved with anything, many problems arise. I say keep the government out and let free enterprise do its job.

Steven W. Ellis

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