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

2.6 Boost Output Ferrite Bead

The ferrite bead FB2 connected at the boost output has a high impedance value at frequencies of around 100 MHz, which can suppress the noise in this frequency range and help reduce the conducted/radiated EMI, as shown in Figure 18 and Figure 19.

LP8866-Q1 snva964-re-boost-FB.gif
(a) With ferrite bead (b) Without ferrite bead
Figure 18. Radiated Emissions: Boost Output Ferrite Bead
LP8866-Q1 snva964-ce-boost-FB.gif
(a) With ferrite bead (b) Without ferrite bead
Figure 19. Conducted Emissions: Boost Output Ferrite Bead