SLVAEX2 September   2020  – MONTH  TPS55288 , TPS55288-Q1 , TPS552882 , TPS552882-Q1

 

  1.   Trademarks
  2. 1Introduction
  3. 2Design Process
    1. 2.1 Radiation Theory
    2. 2.2 Root Cause of the Broad Band EMI in a Buck-Boost Converter
    3. 2.3 How to Achieve Low EMI with TPS55288 Buck-Boost Converter
      1. 2.3.1 Adding Ground Planes under the Critical Loops
      2. 2.3.2 Using Symmetrical Layout Configuration
      3. 2.3.3 Using Frequency Dithering Function
      4. 2.3.4 Adding RC Snubbers at the Switching Node
      5. 2.3.5 Adding Filters at the Input and Output Side
  4. 3Schematic and Test Result
    1. 3.1 Test Result
  5. 4Summary
  6. 5References

4 Summary

The major radiation sources in a buck-boost converter are the input and output switching loops. These critical loops should be as small as possible in order to reduce the radiation. We can reduce the switching loop by proper components placement. Putting a solid ground plane with minimum dielectric thickness under the switching loop can further reduce the equivalent switching loop. With the same component placement and same test condition, the radiated EMI is improved by more than 15dBuV/m with a 4-layer PCB. If the PCB size is not a limit, symmetrical placement of the decoupling capacitors can be adopted to achieve magnetic field cancellation. Frequency dithering technique is very helpful for the average EMI noise level reduction, it spread out the narrow band noise to a broad band noise, the average noise level gets much lower comparing to the no frequency dithering condition. For the high power and high frequency applications, adding a filter at the DC input side and output side also helps.