SNVAA93 December   2023 LM65645-Q1 , LM70660 , LM706A0 , LM706A0-Q1 , LM70840 , LM70840-Q1 , LM70860 , LM70860-Q1 , LM70880 , LM70880-Q1 , LMR38020-Q1 , LMR38025-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Conducted Emission Model of Buck Converters
    1. 2.1 DM Noise Emission Model
    2. 2.2 CM Noise Emission Model
  6. 3Reducing Conducted EMI of Buck Converter in 48V DC Power rail
    1. 3.1 Bead Consideration
    2. 3.2 Layout Consideration
    3. 3.3 Power Inductor Consideration
    4. 3.4 Spread Spectrum
  7. 4Summary
  8. 5References

Abstract

This application note discusses some of the challenges of EMI (electromagnetic interference) in buck converters particularly in automotive systems where the power rail is increasing to 48V DC. The higher rates of change in voltage (dv/dt) and current (di/dt) in the buck converter make it more difficult to meet conducted EMI compliance. This application note discusses the composition and generation of conducted EMI noise in buck converters, using an emission model. To address these EMI related concerns, several methods and techniques were implemented to help designers mitigate conducted EMI issues in a buck regulator. Layout tips, inductor selection, ferrite bead optimization and spread spectrum are discussed in this article.