SPRADB7 September   2023 AM2431 , AM2432 , AM2434 , AM2631 , AM2631-Q1 , AM2632 , AM2632-Q1 , AM2634 , AM2634-Q1 , AM263P4 , AM263P4-Q1 , AM2732 , AM2732-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
    1. 1.1 How to Use This Application Note
    2. 1.2 Glossary
  5. 2Thermal Resistance Overview
    1. 2.1 Junction Vs. Ambient Temperature
    2. 2.2 Package Defined Thermal Resistance Characteristics
    3. 2.3 Board Defined Thermal Resistances
  6. 3Board Design Choices that Affect Thermal Performance
    1. 3.1 Thermal Vias
    2. 3.2 Board Size
    3. 3.3 Air Flow, Heat Sinking, and Enclosures
    4. 3.4 Copper Thickness
    5. 3.5 Relative Position of Heat Emitters
    6. 3.6 Layer Count
    7. 3.7 Breaks in Thermal Pathing
  7. 4Thermal Design Best Practices Review
  8. 5AM263x EVM Thermal Comparison with Data
    1. 5.1 Test Setup and Materials
    2. 5.2 Measurement Logging Software
    3. 5.3 AM263x EVM Comparison
    4. 5.4 Measurement Results
      1. 5.4.1 Lid Temperature Readings
      2. 5.4.2 Power Readings over Temperature
      3. 5.4.3 Calculated Thermal Resistance Values
      4. 5.4.4 Recorded Junction and Ambient Temperatures
      5. 5.4.5 Calculated Junction Temperature at Ambient Temperature Extremes
  9. 6Using the Thermal Model
  10. 7References

2.3 Board Defined Thermal Resistances

The design of a PCB will have a strong correlation to the difference between junction and ambient temperature. The ideal goal is for the junction temperature to be as close as possible to the ambient temperature but when the heat is not able to efficiently diffuse away from the SoC, then the delta between junction and ambient temperature will be larger. The thermal resistance between the board and ambient temperature can be broken up into four separate thermal resistances that will have varying values based on the system design:

  • Thermal resistance of a thermal via (RΘVia)
  • Thermal resistance of a copper plane (RΘCu)
  • Thermal resistance of FR-4 Laminate (RΘFR-4)
  • Thermal resistance of board surface area and ambient temperature (RΘSA)

GUID-0CE8D847-6AE8-4AE0-8CEC-B3F1FCDCA580-low.png Figure 2-4 Breakdown of RΘBA

It is easy to imagine how some simple design choices can help with decreasing the RΘBA which subsequently decreases the RΘJA. A few examples of design choices to help with thermal performance are increasing copper volume of thermal vias, adding additional copper layers, or increasing board size. For a fullbreak down of design choices that affect thermal performance, refer to Section 3.