The Engineer’s Guide To EMI In DC-DC Converters (Part 18): Advanced Spread-Spectrum Techniques
by Timothy Hegarty, Texas Instruments, Phoenix, Ariz., How2Power Today, Jul 15 2021
Focus:
This article describes an enhanced multirate spread-spectrum technique developed by Texas
Instruments that suppresses both acoustic and electromagnetic noise using a combination of
periodic and pseudo-randomized modulations. This hybrid technique, known as dual random
spread-spectrum, enhances EMI performance across the multiple resolution bandwidth
settings specified in automotive EMC tests such as CISPR 25 and EN 55025. This multirate
spread-spectrum technique is implemented in a new synchronous buck controller IC, the
LM25148-Q1. A design example based on this controller is presented here, demonstrating the
impact of the technique in attenuating noise across the low and high frequency ranges
specified in CISPR 25 conducted emissions testing.
What you’ll learn:
- How to achieve EMC compliance in dc-dc converters using TI’s dual random spread-spectrum modulation technique
- How to understand the impact of modulating frequency on the effectiveness of spread spectrum modulation in achieving EMC compliance
- How to understand how tradeoffs in modulating frequency selection and RBW setting in the different EMI test bands motivated the development of the dual random spread-spectrum modulation technique
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