SNLA224A June   2014  – January 2024 DS90UB913A-Q1 , DS90UB954-Q1 , DS90UB960-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Theory of Operation for Power Over Coax
    1. 2.1 Inductor Characteristics
    2. 2.2 Capacitor Characteristics
    3. 2.3 Ferrite Bead Characteristics
  6. 3Design Considerations
    1. 3.1 Frequency Range
    2. 3.2 Power Considerations
    3. 3.3 Inductor Size Considerations
    4. 3.4 Layout Considerations
  7. 4FPD-Link PoC Requirements
    1. 4.1 Channel Requirements
    2. 4.2 PoC Noise Requirements
      1. 4.2.1 VPoC Noise and Pulse
      2. 4.2.2 RIN+ Noise
      3. 4.2.3 Causes of PoC Noise
      4. 4.2.4 Noise Measurement Best Practices
      5. 4.2.5 Reducing Effects of PoC Noise
  8. 5TI Recommended PoC Networks
    1. 5.1 PoC Network From FPD-Link III Data Sheet
    2. 5.2 Murata Networks
      1. 5.2.1 Murata Network 1
      2. 5.2.2 Murata Network 2
      3. 5.2.3 Murata Network 3
    3. 5.3 TDK Networks
      1. 5.3.1 TDK Network 1
      2. 5.3.2 TDK Network 2
      3. 5.3.3 TDK Network 3
      4. 5.3.4 TDK Network 4
      5. 5.3.5 TDK Network 5
      6. 5.3.6 TDK Network 6
      7. 5.3.7 TDK Network 7
      8. 5.3.8 TDK Network 8
    4. 5.4 Coilcraft Networks
      1. 5.4.1 Coilcraft Network 1
      2. 5.4.2 Coilcraft Network 2
      3. 5.4.3 Coilcraft Network 3
      4. 5.4.4 Coilcraft Network 4
  9. 6Summary
  10. 7References
  11. 8Revision History

2.3 Ferrite Bead Characteristics

As the frequency of FPD-Link communications rise, the need for more complex PoC networks follows. Ferrite beads can help greatly when dealing with extremely high frequencies. Ferrite beads are special kinds of inductors that have very low inductance but are rated for frequencies in the MHz to GHz range. Where standard coil inductors typically begin behaving like a capacitor, a ferrite bead can continue to provide high impedance. Figure 2-8 shows a real-world ferrite bead that has an inductive component, capacitive component, and resistive components. The Ferrite bead is primarily inductive, therefore LFB is the most dominant portion of this model. The parasitic capacitance CPar does not become significant until very high frequencies.

GUID-20230712-SS0I-Z7L3-9VF7-C2BGWRXJ2NZ1-low.svg Figure 2-8 Real-World Ferrite Bead

Adding ferrite beads to the PoC network can result in broader frequency coverage. However, a ferrite bead can have a higher resistive component at DC than a standard coil inductor. While the resistance is typically rather small (<1Ω), higher DC resistance can result in significant IR drop in applications where current is drawn.