SLOA343 August   2024 TPS543820 , TPS543A22 , TPSM843620 , TPSM843A22

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Layout Techniques to Reduce EMI
    1. 2.1 Placement of Passive Components
    2. 2.2 Ground Flooding
    3. 2.3 Minimize Number of Antennas
    4. 2.4 Via Stitching
    5. 2.5 Additional Steps to Minimize Impedance or Noise
  6. 3Designing for EMI-Optimized Layout
  7. 4Test Results for Radiated Interference
  8. 5EMI Filtering
  9. 6Summary
  10. 7References

EMI Filtering

To help reduce conducted EMI at the switching frequency of our boards, we tested the effects of two different input filter types:

  • A ferrite bead-based pi filter
  • An Inductor-based pi filter

The pi filter is shown in Figure 5-1, with the ferrite bead or inductor between two capacitors.

 Example pi Filter With Ferrite
                    Bead Figure 5-1 Example pi Filter With Ferrite Bead

Simulated bode plots for the ferrite bead pi filter are shown in (Figure 5-2) and inductor pi filter (Figure 5-3).

Figure 5-3 shows that the ferrite bead filter has the max attenuation occurring at just over 1MHz, after which the attenuation begins to flatten out, while the inductor filter similarly has the max attenuation occurring at just over 1MHz, after which the attenuation begins to flatten out.

 Bode Plot for Ferrite Bead
                        pi FilterFigure 5-2 Bode Plot for Ferrite Bead pi Filter
 Bode Plot for Inductor pi
                        FilterFigure 5-3 Bode Plot for Inductor pi Filter

We tested the simulation results with a series of conducted emissions tests, with the test setup shown in Figure 5-4. In the following conducted EMI data, for the frequencies below 2MHz, the inductor filter caused significantly more improvement to the conducted EMI than the ferrite bead filter. At the switching frequency of 500khz, the 2.2uH inductor filter created 35dB more attenuation.

 Conducted Emissions Test
                    Setup Figure 5-4 Conducted Emissions Test Setup
 TPS543820 Conducted EMI
                        Results With Ferrite Bead FilterFigure 5-5 TPS543820 Conducted EMI Results With Ferrite Bead Filter
 TPSM843620 Conducted EMI
                        Results With Ferrite Bead FilterFigure 5-7 TPSM843620 Conducted EMI Results With Ferrite Bead Filter
 TPS543A22 Conducted EMI
                        Results With Ferrite Bead FilterFigure 5-9 TPS543A22 Conducted EMI Results With Ferrite Bead Filter
 TPSM843A22 Conducted EMI
                        Results With Ferrite Bead FilterFigure 5-11 TPSM843A22 Conducted EMI Results With Ferrite Bead Filter
 TPS543820 Conducted EMI
                        Results With Inductor FilterFigure 5-6 TPS543820 Conducted EMI Results With Inductor Filter
 TPSM843620 Conducted EMI
                        Results With Inductor FilterFigure 5-8 TPSM843620 Conducted EMI Results With Inductor Filter
 TPS543A22 Conducted EMI
                        Results With Inductor FilterFigure 5-10 TPS543A22 Conducted EMI Results With Inductor Filter
 TPSM843A22 Conducted EMI
                        Results With Inductor FilterFigure 5-12 TPSM843A22 Conducted EMI Results With Inductor Filter