Technology Edge

April 2010 Edition

The Technology Edge is a monthly online technical publication that features articles written by National Semiconductor's Engineers. These articles discuss National products, applications and techniques for solving your analog and mixed-signal design challenges, as well as other pertinent technical information.

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AN-2052: National Semiconductor's SIMPLE SWITCHER® Power Modules and EMI

Overview: Power supply design, even the design of common DC to DC switching convertors can present a number of challenges; this is especially true with higher power designs. Beyond the functional issues, an engineer must make sure the design is robust, meets the required cost targets and thermal and space constraints all while staying on schedule. Additionally, and hopefully not as an afterthought, the design must produce sufficiently low Electromagnetic Interference (EMI) both for reasons of product compliance and system performance. However, a power supply's EMI level is one of the more difficult aspects of the design to accurately predict. Some might even argue that it's simply impossible and the best a designer can do is take sufficient care in the design especially in the layout.

While the principles discussed in this article apply more broadly to power design, we're going to focus on DC to DC convertor design given its broad application. It affects virtually every hardware engineer who at some point has to design a power convertor. In this article we'll consider two common trade-offs related to low EMI design; thermal performance and EMI and also solution size related to PCB layout and EMI.