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

2.3.2 Using Symmetrical Layout Configuration

EMI performance can be improved by minimizing the critical switching loops and by adding ground planes under the critical switching loops. If the test result is still over the limit, then other solutions like slowing down the switching speed, adding a metal shield over the power supply circuit should be considered. But slowing down the switching speed will sacrifice the efficiency, adding a metal shield will increase the cost and make the system assembly more complex.

Using symmetrical placement of the decoupling capacitors can further improve the EMI performance without sacrifice the efficiency or increase the cost. Figure 2-6 and Figure 2-7 show the schematic and the related PCB layout of this symmetrical placement concept.

GUID-20200826-CA0I-MBX5-7QZT-BKQXN73ZPKVW-low.png Figure 2-6 Symmetrical PCB Layout of TPS55288 Buck-Boost Converter

Figure 2-7 shows the radiated EMI result with symmetrical placement and without the symmetrical placement. Symmetrical placement helps reduce the radiated EMI in the 200MHz -600MHz high frequency range, the radiated EMI is improved by more than 6dBuV/m with symmetrical placement.

GUID-20200826-CA0I-MW7X-4KS2-ZFTBJJNTRKCW-low.png Figure 2-7 Radiated EMI Comparison with Symmetrical Placement