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

4 GaN converter IC design and implementation

The 48VIN, 960W Four-Phase Buck Converter with Integrated GaN Reference Design was used to evaluate the thermal-focused design considerations. Distributing the load across four interleaved integrated GaN phases reduces the current and power dissipation in each phase while simultaneously supporting high output-current capability and compact solution size that 48V power conversion requires. Table 1 lists the overall design specifications.

Table 1 Buck converter design specifications
Design parameters Value
Input voltage 48V (36V to 60V)
Output voltage 12V
Output current 80A (electrical design and thermal design current)
Topology Four-phase synchronous buck
Switching frequency 400kHz (each phase)
Power stage Four LMG708B0 devices
Reference design number PMP23595

To evaluate the resulting temperature distribution and heat flow through the package, cooling structure, and PCB a thermal simulation was conducted. The thermal simulation was created using Ansys Icepak® thermal modeling software tool. Figure 2 shows the steady-state thermal simulation of the four-phase buck converter at the full 960W output at an ambient temperature of 25℃ with no airflow, and 6.29W of power dissipation assigned to each of the four LMG708B0 devices. The power dissipation was calculated by obtaining the total power losses of the reference design at the full 960W output under the 25℃ ambient temperature condition and subtracting the losses generated from the surrounding passives, leaving only the losses generated by the LMG708B0 devices. The device power dissipation corresponded to 25.16W of total power dissipation across the four phases. The simulated package temperatures are approximately 108℃ across the four phases, still well below the recommended case temperature of the LMG708B0 device, which is 135℃.


Thermal simulation of the four integrated GaN power stages with the dual-side cooling structure

Figure 2 Thermal simulation of the four integrated GaN power stages with the dual-side cooling structure

The simulation also illustrates the thermal paths from the integrated GaN devices through both the dual-side cooling structure and the PCB. However, the simulation represents an approximation of the final hardware implementation. The modeled heat-sink geometry differs slightly from the final heat sink and does not account for the thermal interface material (TIM) used between the LMG708B0 packages and the heat sink. The TIM introduces additional case-to-sink thermal impedance that can affect the overall thermal performance of the dual-side cooling path. Therefore, the simulated temperatures provide a thermal reference for comparison with the measured converter performance discussed later in the article.