TIDUF22 January   2023

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1  6-W Auxiliary Power Supply
      2. 2.2.2  AC Input Current Sensing
      3. 2.2.3  DC Bus Voltage Sensing
      4. 2.2.4  AC Input Voltage Sensing
      5. 2.2.5  GaN Driving
      6. 2.2.6  Inrush Current Protection at Powering On
      7. 2.2.7  Overcurrent Protection
      8. 2.2.8  AC Input Undervoltage Protection
      9. 2.2.9  DC Bus Overvoltage Protection
      10. 2.2.10 GaN Temperature Monitor and Protection
      11. 2.2.11 Heat Sink Temperature Monitor and Protection
      12. 2.2.12 UART Heartbeat Report
      13. 2.2.13 Motor Control Interface
    3. 2.3 Highlighted Products
      1. 2.3.1 LMG352xR030
      2. 2.3.2 TMS320F28002x
      3. 2.3.3 UCC2871x
      4. 2.3.4 TLV906x
      5. 2.3.5 TPS54308
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements and Assembly
      1. 3.1.1 Test Equipment Requirements
    2. 3.2 Software Requirements
    3. 3.3 Test Setup
    4. 3.4 Test Results
      1. 3.4.1 Test Procedures
        1. 3.4.1.1 Test Procedures Under 90 VAC
        2. 3.4.1.2 Test Procedures Under 220 VAC
    5. 3.5 Performance Data: Efficiency, iTHD, and Power Factor
    6. 3.6 Functional Waveforms
      1. 3.6.1  Test Under 90 VAC, 800-Ω Load
      2. 3.6.2  Power-On Sequence Test Under 220 VAC
      3. 3.6.3  Waveform With Heavy Load
      4. 3.6.4  Buck Auxiliary Power Supply Tests
      5. 3.6.5  AC Drop Test
      6. 3.6.6  GaN Switching Performance
      7. 3.6.7  Thermal Test
      8. 3.6.8  Power-Off Sequence
      9. 3.6.9  Surge Test
      10. 3.6.10 Conducted Emission Test
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Documentation Support
    3. 4.3 Support Resources
    4. 4.4 Trademarks
  10. 5About the Author

3.6.7 Thermal Test

Thermal performance is validated in this design. The conditions are as shown in the following list:

  • 200 VAC with 4-kW load
  • Cooling fan: 27CFM, 24 V, 2.64 W
  • Thermal balanced after 15 minutes
  • Ambient temperature is 25°C

Figure 3-17 shows the test setup for the temperature rising test.

GUID-20221130-SS0I-7S7M-4KSM-WCCNP5XXGW0W-low.pngFigure 3-17 Thermal Test setup

Figure 3-18 shows boost inductor temperature at 200 VAC, 4 kW, temperature rising is 69.6°C – 25°C = 44.6°C.

GUID-20221130-SS0I-4F9D-SMDV-HWVMX0L5LMGR-low.pngFigure 3-18 Boost Inductor Temperature

Since the GaN daughterboard is underneath the main board, measuring the GaN temperature rising with a thermal imager is difficult. However, GaN reports the temperature at the TEMP pin in PWM mode, and the PWM duty ratio represents temperature. Firmware monitors the PWM duty ratio, and calculates temperature, and reports this information to the host PC through the UART port. Figure 3-19 is the heartbeat report on the UART terminal. The temperature of GaN can be read in the report.

For some applications with even lower AC input voltage, the input current is higher, so temperature rising of GaN, diode bridge, and boost inductor is even higher. Users must fully evaluate temperature rising of those devices, to make sure the devices have enough temperature rising margin.

GUID-20221130-SS0I-CWBZ-FSSF-1DGDRFXX92CJ-low.pngFigure 3-19 GaN Temperature Rising on Heartbeat Report