TIDUF28 November   2023

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Highlighted Products
      1. 2.2.1 LMG3422R030
      2. 2.2.2 ISO7741
      3. 2.2.3 AMC1306M05
      4. 2.2.4 AMC1035
      5. 2.2.5 TPSM560R6H
      6. 2.2.6 TPSM82903
  9. 3System Design Theory
    1. 3.1 Power Switches
      1. 3.1.1 GaN-FET Selection Criterion
      2. 3.1.2 HVBUS Decoupling and 12-V Bootstrap Supply
      3. 3.1.3 GaN_FET Turn-on Slew Rate Configuration
      4. 3.1.4 PWM Input Filter and Dead-Time Calculation
      5. 3.1.5 Signal Level Shifting
      6. 3.1.6 LMG3422R030 Fault Reporting
      7. 3.1.7 LMG3422R030 Temperature Monitoring
    2. 3.2 Phase Current Sensing
      1. 3.2.1 Shunt
      2. 3.2.2 AMC1306M05 Analog Input-Filter
      3. 3.2.3 AMC1306M05 Digital Interface
      4. 3.2.4 AMC1306M05 Supply
    3. 3.3 DC-Link (HV_BUS) Voltage Sensing
    4. 3.4 Phase Voltage Sensing
    5. 3.5 Control Supply
    6. 3.6 MCU Interface
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Hardware Requirements
      1. 4.1.1 PCB
      2. 4.1.2 MCU Interface
    2. 4.2 Software Requirements
    3. 4.3 Test Setup
      1. 4.3.1 Precautions
      2. 4.3.2 Test Procedure
    4. 4.4 Test Results
      1. 4.4.1 24-V Input Control Supply
      2. 4.4.2 Propagation Delay PWM to Phase Voltage Switch Node
      3. 4.4.3 Switch Node Transient at 320-VDC Bus Voltage
      4. 4.4.4 Phase Voltage Linearity and Distortion at 320 VDC and 16-kHz PWM
      5. 4.4.5 Inverter Efficiency and Thermal Characteristic
        1. 4.4.5.1 Efficiency Measurements
        2. 4.4.5.2 Thermal Analysis and SOA Without Heat Sink at 320 VDC and 16-kHz PWM
  11. 5Design and Documentation Support
    1. 5.1 Design Files
      1. 5.1.1 Schematics
      2. 5.1.2 BOM
      3. 5.1.3 PCB Layout Recommendations
        1. 5.1.3.1 Layout Prints
      4. 5.1.4 Altium Project
      5. 5.1.5 Gerber Files
      6. 5.1.6 Assembly Drawings
    2. 5.2 Tools and Software
    3. 5.3 Documentation Support
    4. 5.4 Support Resources
    5. 5.5 Trademarks
  12. 6About the Author

4.4.5.1 Efficiency Measurements

The efficiency testing was done at 27°C lab temperature with a Tektronix PA4000 power analyzer. The TIDA-010255 PCB without heat sink was placed horizontal on the workbench as shown in Figure 4-4, with natural convection only. The F28379D MCU software was configured to create a 3-phase AC voltage at 1-Hz frequency with configurable amplitude. The PWM carrier frequency was set to either 16 kHz or 8 kHz.

The following figures show the TIDA-010255 PCB power losses without heat sink versus the 3-phase motor load current in ARMS in the steady state, when the PCB and the GaN-FETs reach their steady state temperature, typically after around 5 minutes. The power losses are dominated by the switching and conduction power losses of GaN-FET, while the phase current shunt power losses are negligible.

GUID-20231101-SS0I-HJJC-GWFQ-RZ4RL223WGRJ-low.svg Figure 4-19 TIDA-010025 Power Losses at 320 VDC, 8-kHz and 16-kHz PWM versus Output Current

The TIDA-010255 board power losses at an output current of 7.7 ARMS at 16-kHz PWM were 16.09 W, and 11.2 W at 8-kHz PWM.

The theoretical maximum peak efficiency at 320 VDC with a maximum phase-to-phase of voltage of 130 VRMS (Space Vector PWM with 3rd harmonics) and a power factor of 0.9 is 99.4% at 16-kHz PWM and 99.6% at 8-kHz PWM.

GUID-20231101-SS0I-2SCS-L99L-H1DB6BRMHVS9-low.svg Figure 4-20 Calculated Maximum Peak Efficiency at 320 VDC, 8-kHz and 16-kHz PWM

To see the effective parasitic capacitive losses, the TIDA-010255 PCB power losses were measured at zero load current with 50% PWM duty cycle and PWM switching frequencies from 8 kHz to 64 kHz, as shown in Figure 4-21. In the first test the inverter output was left unconnected. The losses at 64-kHz PWM were 21.7 W. The total losses are per Equation 5, where COSS_HB is the effective parasitic capacitance per half-bridge of around 1.1 nF, which gives around 550 pF per each of the six power switches including TIDA-010255 PCB parasitic capacitance. Assuming a 50-pF parasitic PCB capacitance, the estimated time related effective output capacitance CO(tr) of the LMG3422R030 from 0 V to 320 V is around 500 pF, which is around 15% higher than the 430-pF CO(tr) from 0 V to 400 V.

In the second test an AC induction motor with a 1-m cable was connected to explore the impact on the overall zero load current losses. Again, the PWM duty cycle was set to 50%, hence no motor current was driven. The losses at 64 kHz increased to 22.7 W. The additional parasitic load capacitance with the 1-m cable an AC induction motor was calculated around 50 pF per phase.

Equation 5. COSSHB=13×PNOLOADVDC2×fPWM
GUID-20231101-SS0I-9ZWK-5FL5-62VKKPCX8ZNT-low.svg Figure 4-21 TIDA-010025 Power Losses at 320 VDC Without Heat Sink versus PWM Frequency at No Load