SLUP412 February   2022 LMG3522R030-Q1


  1. Introduction
  2. Comparing Different Technologies
  3. Advantages of Integrating the Driver With GaN FETs
  4. The GaN-Based 6.6-kW OBC Reference Design
  5. PFC Stage
  6. DC/DC Stage
  7. DC/DC Topology Selection
  8. Frequency Selection
  9. Core Loss
  10. 10Loss of ZVS
  11. 11Dead Time
  12. 12ISR Bandwidth
  13. 13Overall
  14. 14Resonant Tank Design
  15. 15Thermal Solution
  16. 16Layout Best Practices
  17. 17Control-Loop Considerations
  18. 18Conclusions
  19. 19References
  20. 20Important Notice


The first generations of onboard chargers (OBCs) leveraged insulated gate bipolar transistors (IGBTs) and were huge and bulky. Figure 1-1 illustrates the improvement in solution size with better technologies and thermal concepts.

GUID-20220218-SS0I-GSMW-D7SV-QJKJNT7FS1FC-low.jpg Figure 1-1 Second-generation SiC-based OBC reference designs [1] (light-blue frame, convection-cooled) and a third-generation GaN-based OBC reference design (green frame, liquid-cooled).

GaN’s ultra-fast switching slew rates and liquid-cooled thermal interface yield a 22% reduction in size (area: 38,171 mm2) [2] compared to the convection-cooled SiC-based DC/DC and power factor correction (PFC) reference designs on the left [3] and right [4] inside the light-blue frame in Figure 1-1, respectively. Texas Instruments (TI) had designed these latter two reference designs (area: 27,886 mm2 + 20,915 mm2) three years earlier than the reference design in the green frame. This topic explains the design process behind the GaN-based reference design in the green frame.