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

3.1.7 LMG3422R030 Temperature Monitoring

The TEMP pin of each LMG3422R030 is a push-pull digital output that gives information about the GaN FET junction temperature. The LMG342R030 TEMP pin outputs a fixed 9-kHz pulsed waveform. The device junction temperature is encoded as the duty cycle of the PWM waveform. The PWM duty cycle is around 3% at a temperature of 25°C and 82% at a temperature of 150°C. For temperatures above 150°C, the duty cycle continues to increase linearly until overtemperature fault occurs. When an overtemperature fault occurs, the TEMP pin is pulled high to indicate this fault. There is a hysteresis to clear overtemperature fault.

The TEMP signals are level shifted from 5 V to 3.3 V for each of the six LMG3422R030 devices, as shown in Section 3.1.4. In this design, only the PWM temperature signals of the phase V half-bridge TOP_TEMP_V and BOT_TEMP_V are available to the MCU. A 1.5-kHz low-pass filter with R13 (R33) and C20 (C47) attenuates the 9-kHz PWM carrier before the two signals are routed to the C2000 controlCARD connector J1 and the MCU header J7. For more precise temperature sensing, offset and gain calibration as well as over-sampling through an ADC integrated on the MCU are recommended. Equation 3 shows a simplified transfer function to calculate the LMG3422R030 junction temperature form the low-pass filtered TEMP PWM signal, assuming a 3.3-V supply voltage.

Equation 3. TjLMG3422°C=TOP_TEMP_VV-0.099V2.607[V]×125°C+25°C