SNVA951 November   2020 LM61460-Q1 , LM63615-Q1 , LM63625-Q1 , LM63635-Q1 , LMR33620-Q1 , LMR33630-Q1

 

  1.   Trademarks
  2. 1 Introduction
  3. 2 The Goal of Thermal Management
  4. 3 Junction Temperature Calculation
    1. 3.1 Regulator Junction Temperature (TJ)
    2. 3.2 Ambient Temperature (TA)
    3. 3.3 Power Dissipation (PD)
    4. 3.4 Thermal Resistance (θJA)
      1. 3.4.1 Thermal Metrics
  5. 4 Package Type
  6. 5 PCB Copper Heat Sink
  7. 6 PCB Layout Tips
  8. 7 Estimating and Measuring θJA
    1. 7.1 Simple Guideline
    2. 7.2 Data Sheet Curves
    3. 7.3 Simplified Heat Flow Spreadsheet
    4. 7.4 Online Database
    5. 7.5 Thermal Simulators
  9. 8 Measuring Thermal Performance
    1. 8.1 Thermal Camera
    2. 8.2 Thermocouple
    3. 8.3 Internal Diode
  10. 9 Thermal Design Example
  11. 10Conclusion
  12. 11References

8.2 Thermocouple

A thermocouple (TC) can be used to measure the regulator case temperature as well. This method is more complicated and time consuming than using a camera. The TC must be much smaller than the package you are probing and needs to make good thermal contact. If the TC is too large it will act as a heatsink and lower the actual temperature of the package. You also need to position the probe as close as possible to the die within the package. Equation 6 is then used to estimate the junction temperature, with the TC measurement in place of
Tcamera. The TC can also be placed on the PCB to estimate its temperature. The ΨJB parameter can then be used to estimate junction temperature from the board temperature, but this method is not as accurate as using the top case temperature. See Semiconductor and IC Package Thermal Metrics Application Report, for more details.