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

3 Reducing Conducted EMI of Buck Converter in 48V DC Power rail

Section 2 presented the propagation path and emission model for both differential mode (DM) noise and common mode (CM) noise of the buck converter. By understanding these factors, EMI issues can be addressed by minimizing noise sources and interfering propagation paths. The EMI tests conducted follow the CISPR 25 Class 5 standard. In this study, the LMR38020-Q1 is used, which is an 80 V, 2 A synchronous buck converter. The schematic of the converter is shown in Figure 3-22. The test conditions include Vin=48 V, Vout=5 V, Iout=2 A, and Fsw=400 kHz, which are typical parameters for a DC-DC power system in an automotive setting.

GUID-20231107-SS0I-FR5H-QLQS-HBRWPGWXN3KL-low.pngFigure 3-1 Buck Converter Schematic with EMI Filter and Bead