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

1 System Description

AC input 3-phase inverters with high energy efficiency up to IEC 61800-9 energy class IES2 not only help reduce the global energy footprint, but also enable smaller form factor and higher power density designs with reduced heat sink size. Form factor and weight play an important role, especially with motor-integrated servo drives used in industrial robot and factory automation applications where the motors are part of a mechanical moving system, such as a 6-axis robot.

Motor integrated 3-phase inverters are often supplied from single-phase 200- to 230-VAC input, equivalent to a rectified 320 VDC. Input power levels are typically less than 3 kW. Today the vast majority of 230-VAC-input servo drives leverage IGBT-based power switches with PWM switching frequencies from 8 kHz to 16 kHz. Due to the power losses of the insulated-gate bipolar transistors (IGBTs), the size of the heat sink can be more than 30% of the overall 3-phase inverter size.

Gallium nitride (GaN) power transistors help reduce power losses versus IGBTs significantly, even at low pulse-width modulation (PWM) switching frequencies of 8 kHz to 16 kHz. GaN-FETs with integrated drivers, such as the LMG3422R030, reduce both switching and conduction losses and can achieve 99.4% peak efficiency at 16-kHz PWM. This reduces the overall power losses by more than a factor of 4 compared to traditional IGBT-based 3-phase inverters, as shown in this reference design at 7-ARMS output phase current.

The TIDA-010255 reference design realizes a high-efficiency, hot-side MCU controlled 320 VDC, 2-kW, 3-phase, power stage, using six fast switching LMG3422R030 600-V, 30-mΩ GaN-FETs. The LMG3422R030 includes an integrated driver, protection, and temperature reporting and helps increase reliability while reduce the system cost for external protection and temperature monitoring circuits. Buck modules with integrated inductors and bootstrap supplies reduce the footprint for power management and gate drive bias supply. Accurate and high linearity phase current sensing is achieved using 1-mΩ in-phase current shunts with a ±50-mV input, reinforced isolated modulator AMC1306M05. Due to the hot-side control, where the MCU ground (GND) is equal to power GND (DC–), isolation is not required to sense the DC-link voltage and the three phase voltages. A non-isolated AMC1035 delta-sigma modulator measures the DC-link voltage. A non-isolated analog phase voltage feedback option enables advanced sensorless designs like InstaSPIN-FOC using a C2000 MCU with 12-bit integrated ADCs.

For evaluation of TI’s GaN technology with industrial drives, the design offers 3.3-V I/O interface signals with either a 180-pin HSEC connector for use with C2000 MCU controlCARDs, such as the F28379D controlCARD, or standard headers to connect to other MCUs like the Sitara AM2631 or AM2431.

The design was tested without a heat sink at room temperature with a DC-link voltage of 320 VDC and 16-kHz PWM up to 7.7-ARMS continuous 3-phase output current. For testing at higher currents or testing at higher ambient temperature a heat sink can be mounted at the bottom side of the PCB. Mounting holes are provided on the PCB.