SNVA964 June   2020 LP8866-Q1

 

  1.   LP8866-Q1 Typical Design Guidelines to Achieve CISPR 25 Class 5 Conducted and Radiated Emissions Compliance
    1.     Trademarks
    2. 1 Typical Reference Design
      1. 1.1 Design Overview
      2. 1.2 Test Condition
      3. 1.3 CISPR 25 Measurement Results
    3. 2 EMI Mitigation Techniques Discussion
      1. 2.1 Spread Spectrum
      2. 2.2 Gate Resistor
      3. 2.3 LED Current Sink Capacitors
      4. 2.4 Layout Consideration
      5. 2.5 Inductor Selection
      6. 2.6 Boost Output Ferrite Bead
      7. 2.7 Common Mode Filter
    4. 3 Summary

2.7 Common Mode Filter

Since this application report only summaries the techniques to improve radiated and current method conducted EMI, which mainly comes from the common mode noise, it won’t discuss the design of the input differential mode filter, which has been verified to make little difference. The measurement results with and without the common mode choke are shown in Figure 20 and Figure 21.

LP8866-Q1 snva964-re-CM-choke.gif
(a) With common mode choke (b) Without common mode choke
Figure 20. Radiated Emissions: Common Mode Filter
LP8866-Q1 snva964-ce-CM-choke.gif
(a) With common mode choke (b) Without common mode choke
Figure 21. Conducted Emissions: Common Mode Filter