SNLA385 September   2021 DP83561-SP , DP83620 , DP83630 , DP83640 , DP83822H , DP83822HF , DP83822I , DP83822IF , DP83825I , DP83826E , DP83826I , DP83843 , DP83847 , DP83848-EP , DP83848-HT , DP83848C , DP83848H , DP83848I , DP83848J , DP83848K , DP83848M , DP83848Q-Q1 , DP83848T , DP83848VYB , DP83848YB , DP83849C , DP83849I , DP83849ID , DP83849IF , DP83867CR , DP83867CS , DP83867E , DP83867IR , DP83867IS , DP83869HM

 

  1.   Trademarks
  2. 1Introduction
  3. 2IEEE Specification and How to Derive the Formula
  4. 3Formula Helper to Calculate Limit
  5. 4Conclusion and Summary
  6. 5References

4 Conclusion and Summary

This application brief provides a simple and easy method to validate if the test case passes even though the test report shows a test case failure. When the test case fails after validating the formula, further hardware analysis must be made to find the root cause of the failure. From TI experience the following can cause the Ethernet compliance test case to fail:

  • Incorrect formula - check that the formula for the test case is correct using the formula and method described in Section 3.
  • Unsupported transformer - Validate that the transformer used in the design does match with the Ethernet PHYs transformer requirements (see the transformer section in the data sheet and compare it with transformer data sheet and schematics implementation).
  • Layout optimization - Review the Ethernet PHY layout guidelines and recommendations in the PHY data sheet.
  • Transmission line interaction - Cross talk impact of transmission lines by enabling transmit on signal pair only.
  • Drive strength tuning - Some Ethernet PHYs have the capabilities to increase or decrease the transmission drive strength on the MDI interface inside the PHY. Tuning the drive strength per pair can be used to potentially pass the compliance tests.
  • Magnetics decoupling - On the MDI side, capacitors are connected to the center taps of the transformer. Tuning the value of these capacitors may help pass the compliance tests.

Additional components on the MDI routing to Magentics: ESD or other components with high capacitance and impedance added on the path will be evaluated.

Post Ethernet questions to the TI E2E™ forum.