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

7.2 Data Sheet Curves

Many modern converter products include curves in the data sheet of θJA versus copper area. These curves represent actual data measured on dedicated PCBs constructed for this purpose. Devices such as the LMR336x0 and LM636x5-Q1 families provide this data for the packages available for these devices. An example is shown in Figure 5-1. For the assumptions and conditions under which these curves were taken, they give a fairly good estimate of the thermal performance that can be expected. Many times curves of maximum output current vs ambient temperature, called "de-rating" curves, are also included in the data sheet. These curves are taken with an assumed value of θJA and can be used to estimate the maximum output current for a given ambient under the stated conditions.