SNLA466A August   2024  – October 2024 DP83822I , DP83826E , DP83826I , DP83867E , DP83867IR , DP83869HM

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Abbreviation
  5. 2Introduction
  6. 3EMC Emission
    1. 3.1 Radiated Emission
      1. 3.1.1 Test Setup for Radiated Emission Test
      2. 3.1.2 Main Radiated Emission Sources
    2. 3.2 Conducted Emission
      1. 3.2.1 Test Setup for Conducted Emission Test
      2. 3.2.2 Main Conducted Emission Sources
    3. 3.3 Debug Procedure on EMC Emission
      1. 3.3.1 General Debug Procedure
      2. 3.3.2 RE Specific Debug
      3. 3.3.3 CE Specific Debug
  7. 4EMC Immunity Test
    1. 4.1 EMI Passing Criteria
    2. 4.2 Common EMI Knowledge
    3. 4.3 IEC61000 4-2 ESD
      1. 4.3.1 ESD Test Setup
      2. 4.3.2 Possible Root Cause of Failure
      3. 4.3.3 Debug Procedure
        1. 4.3.3.1 Follow the Test Setup
        2. 4.3.3.2 Remove External Factors on Cable or Link Partner
        3. 4.3.3.3 Areas to Explore to Improve ESD Performance
          1. 4.3.3.3.1 Air or Capacitive Coupling Discharge ESD Recommendations
          2. 4.3.3.3.2 Direct Contact Discharge ESD Recommendation
        4. 4.3.3.4 Schematic and Layout Recommendations
    4. 4.4 IEC 61000 4-3 RI
      1. 4.4.1 RI Test Setup
      2. 4.4.2 Possible Root Cause of Failure
      3. 4.4.3 Debug Procedure
        1. 4.4.3.1 Follow RI Test Setup
        2. 4.4.3.2 Remove External Factor on Cable or Link Partner
        3. 4.4.3.3 Found out Main Emission Area
        4. 4.4.3.4 Schematic and Layout Recommendation
    5. 4.5 IEC 61000 4-4 EFT
      1. 4.5.1 EFT Test Setup
      2. 4.5.2 Possible Root Cause of Failure
      3. 4.5.3 Debug Procedure
        1. 4.5.3.1 Follow EFT Test Setup
        2. 4.5.3.2 Remove External Factor on Cable or Link Parnter
        3. 4.5.3.3 Areas to Explore to Improve EFT Performance
        4. 4.5.3.4 Schematic and Layout Recommendation
    6. 4.6 IEC 61000 4-5 Surge
      1. 4.6.1 Surge Test Setup
      2. 4.6.2 Possible Root Cause of Failure
      3. 4.6.3 Debug Procedure
        1. 4.6.3.1 Follow Surge Test Setup
        2. 4.6.3.2 Remove External Factor on Cable or Link Partner
        3. 4.6.3.3 Area to Explore to Improve Surge Performance
        4. 4.6.3.4 Schematic and Layout Recommendation
    7. 4.7 IEC 61000 4-6 CI
      1. 4.7.1 CI Test Setup
      2. 4.7.2 Possible Root Cause of Failure
      3. 4.7.3 Debug Procedure
        1. 4.7.3.1 Follow CI Test Setup
        2. 4.7.3.2 Remove External Factors on Cable or Link Partner
        3. 4.7.3.3 Areas to Explore to Improve CI Performance
        4. 4.7.3.4 Schematic and Layout Recommendation
  8. 5Schematic and Layout Recommendation for All EMC, EMI Tests
    1. 5.1 Schematic Recommendation
    2. 5.2 Layout Recommendation
  9. 6Summary
  10. 7References
  11. 8Revision History

4.2 Common EMI Knowledge

EMI noise can potentially couple to the system in multiple ways: Conductive coupling, Radiative coupling, and so on. Not the importance to understand the types of noise coupled into the system to effectively debug EMI failure and improve the design. The following section outlines potential noise coupling sources in each EMI test, in addition to design suggestions to improve performance.

Some common knowledge and misunderstandings on EMI testing:

Cable type:

Cable types play a significant role in EMI testing. The recommended Ethernet cable type for EMI tests is outlined below:

  • Shielded vs unshielded cable:
    • Shielded cables are often necessary for high-speed digital data transmission in electromagnetic environments. Shielded cables have ground conducted shield wrap around each of the twisted pairs. With shielded cable, most noise coming from external wires can flow through the ground connected shield directly to earth ground, instead of coupling into the signal line. Shielded cable also improves the protection against cross talk, EMI tests, and reduces emissions from the cable.
      Shielded Cable Example Figure 4-1 Shielded Cable Example
Note: Double shielded cable have layer of aluminum foil wrap around each pair of cable and a layer of metal mesh grid which typically have better EMI performance than single shielded cable with only aluminum foil wrap around each pair of cable.
  • CAT 5 vs CAT 6 cable:
    • CAT 6 cable is preferred for better EMI performance. Compared to CAT5E, CAT6 has plastic insulation in the center to isolate each of the twisted pairs. The ground shield around each twisted pair of CAT6 is also thicker than CAT5E.
  • ESD diodes:
    • ESD diodes are often useful to protect the device from being damaged during EMI testing. However, ESD diodes are not a useful approach when Class A performance is required. When the ESD diodes trigger, the MDI lines can clamp to a certain voltage and result in link drop or packet errors. This results in Class B performance. When ESD diodes are implemented during normal applications, they act as capacitors on the MDI lines. If the ESD diodes are not tuned properly, the signal can face attenuation or impedance mismatch on the MDI lines.

The following sections detail the setup and debug procedure for each EMI test, including possible schematic/layout suggestions for improved performance.