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

2 Conducted Emission Model of Buck Converters

The conducted emission model of a buck converter involves understanding the sources and propagation paths of both differential-mode (DM) and common-mode (CM) noise. By understanding these sources, designers can develop mitigation strategies to reduce conducted electromagnetic interference (EMI) noise.

DM noise refers to the noise that flows between the input and output of the converter. It is caused by the switching action of the converter, which results in voltage and current variations. These variations can generate high-frequency noise that can propagate through the input and output circuits. The main sources of DM noise in a buck converter are the switching transistor, the inductor, and the input capacitor.

CM noise, on the other hand, refers to the noise that flows in parallel to the input and output of the converter. It is caused by asymmetries in the converter's layout and parasitic capacitance. CM noise can be induced by the switching action of the converter and can propagate through the ground and power lines. The main sources of CM noise in a buck converter are the parasitic capacitance between the input and output circuits, the ground plane, and the power traces.