SLYT882 October   2026 LMG708B0

 

  1.   1
  2. 1 Introduction
  3. 2 Integrated GaN for high power density conversion
  4. 3 Thermal challenges and dual-side cooling
  5. 4 GaN converter IC design and implementation
  6. 5 Experimental evaluation
  7. 6 Thermal performance
  8. 7 Conclusion
  9. 8 About the author
  10. 9 References
  11. 10Additional resources
  12. 11Trademarks

5 Experimental evaluation

The operating load range for evaluating converter performance was at a 48V input and 12V output. Figure 3 shows the measured efficiency and corresponding power losses as a function of output current. Presenting both quantities provides a more complete view of converter performance. Efficiency indicates the effectiveness of power conversion, whereas the power-loss curve represents the thermal load that the converter must dissipate. To maximize the effect of the dual-side cooling package, a heat sink was attached during data capture with no additional airflow used. Details about the heat sink and the test setup are discussed later in the article.


Measured efficiency and power loss vs output current

Figure 3 Measured efficiency and power loss vs output current

At lighter loads, relatively fixed losses associated with inductor core loss, gate drivers, and other control-related losses represent a larger percentage of the processed power. As the output current increases, these fixed losses become less significant relative to the output power and efficiency improves, reaching a maximum near 40A. Beyond this point, current-dependent losses become increasingly dominant because resistive conduction losses increase approximately with the square of the current (I2R). Conduction losses within the power ICs, inductors, and high current PCB copper paths therefore increase rapidly with load current, resulting in a gradual reduction in efficiency as the converter approaches full load.

Although the efficiency decreases by only 0.5% between the peak efficiency and the maximum load, the corresponding power losses increase by 18.2W. This increase in absolute power losses represents a significant thermal load within the compact converter footprint and reinforces the importance of providing effective heat-removal paths for the power stages and surrounding components.

The measured power-loss data also provides context for the thermal simulation in Figure 2. The simulation assigned 6.29W of dissipation to each LMG708B0 IC, corresponding to 25.16W across the four phases at the 80A full-load operating point. At the measured 80A operating point, the total converter power losses are 31.2W. The difference between these values represents losses distributed among other converter components, mainly inductors and current sense shunt resistors, and PCB current paths, while also reflecting the assumptions used in the thermal model. Nevertheless, the comparison indicates that a substantial portion of the total thermal load is associated with the four integrated GaN power ICs, supporting the use of dedicated dual-side cooling to supplement heat spreading through the PCB.