SLUP412 February   2022 LMG3522R030-Q1

 

  1. 1 Introduction
  2. 2 Comparing Different Technologies
  3. 3 Advantages of Integrating the Driver With GaN FETs
  4. 4 The GaN-Based 6.6-kW OBC Reference Design
  5. 5 PFC Stage
  6. 6 DC/DC Stage
  7. 7 DC/DC Topology Selection
  8. 8 Frequency Selection
  9. 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

1 Introduction

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.