TIDUF68 February   2024

 

  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 Design Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1 LMG2100
      2. 2.3.2 INA241A
      3. 2.3.3 LMR38010
  9. 3System Design Theory
    1. 3.1 Three-Phase GaN Inverter Power Stage
      1. 3.1.1 LMG2100 GaN Half-Bridge Power Stage
    2. 3.2 Inline Shunt Precision-Phase Current Sensing With INA241A
    3. 3.3 Phase Voltage and DC Input Voltage Sensing
    4. 3.4 Power-Stage PCB Temperature Monitor
    5. 3.5 Power Management
      1. 3.5.1 48V to 5V DC/DC Converter
      2. 3.5.2 5V to 3.3V Rail
    6. 3.6 Interface to Host MCU
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Hardware Requirements
      1. 4.1.1 TIDA-010936 PCB Overview
      2. 4.1.2 TIDA-010936 Jumper Settings
      3. 4.1.3 Interface to C2000™ MCU LaunchPad™ Development Kit
    2. 4.2 Software Requirements
    3. 4.3 Test Setup
    4. 4.4 Test Results
      1. 4.4.1 Power Management and System Power Up and Power Down
    5. 4.5 GaN Inverter Half-Bridge Module Switch Node Voltage
      1. 4.5.1 Switch Node Voltage Transient Response at 48V DC Bus
        1. 4.5.1.1 Output Current at ±1A
        2. 4.5.1.2 Output Current at ±10A
      2. 4.5.2 Impact of PWM Frequency to DC-Bus Voltage Ripple
      3. 4.5.3 Efficiency Measurements
      4. 4.5.4 Thermal Analysis
      5. 4.5.5 No Load Loss Test (COSS Losses)
  11. 5Design and Documentation Support
    1. 5.1 Design Files {Required Topic}
      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
  13. 7Recognition

1 System Description

Low-voltage 12V to 60V DC-fed three-phase inverters in the power range of 1.5kW are used in many applications such as collaborative robots, automated mobile robots, automated guide vehicles (AGV), servo and non-military drones.

In many of these applications the power electronics is motor integrated and hence has a small form factor. High power efficiency and power density are critical parameters to build smaller and lesser weight collaborative robots with a reduced size and no heat sink.

Higher pulse-width modulation (PWM) switching frequencies up to 100kHz help reduce the DC-bus capacitor; therefore reducing size and height by replacing electrolytic with ceramic capacitors. In addition, higher PWM switching frequencies are desired to reduce the current and hence torque ripple of the motor, especially with low inductance brushless AC motors for more precise control.

Conversely, the inverter losses increase with the switching frequency. With a traditional low-voltage 48V silicon field-effect transistor (Si-FET) inverter, the switching losses at 40kHz PWM can already be significantly higher than the conduction losses and hence dominate the overall power losses. To dissipate the excess heat, a larger heat sink is required. However, the heat sink increases system cost, weight, and space.

The solution to the problem is to use GaN FETs, which have several advantages over Si-FETs. Gallium nitride (GaN) transistors can switch much faster than silicon MOSFETs, thus having the potential to achieve lower switching losses. At high slew rates; however, certain package types can limit GaN FET switching performance. Integrating the GaN FET and driver in the same package reduces parasitic inductances and optimizes switching performance.

The TIDA-010936 reference design has a small form factor, three-phase inverter with three 100V, 35A half-bridge GaN power modules LMG2100R044. The LMG2100R044 integrates the driver and two 80V GaN FETs in a small 5.5mm × 4.5mm QFN package, optimized for extremely low gate loop and power loop impedance. The PCB offers mounting holes for an optional heat sink with the top-side cooled LMG2100R040 GaN-FET power modules. An integrated bootstrap diode helps further reduce space for the high-side GaN-FET bias supply.

For precision and small form factor phase current measurements with high linearity, the reference design employs a low impedance 1mΩ phase current shunt and a differential precision current sense amplifier INA241 with high common mode and high AC common mode transient immunity due to the INA241 integrated PWM rejection. The measurement range is ±33A and is converted into a unipolar output voltage from 0V to 3.3V with a bias voltage of 1.65V for zero current.

The three-phase GaN inverter offers a hardware-based short-circuit projection using high-side DC-link shunt with a high common mode window comparator with a configurable overcurrent threshold, which turns off the PWM buffer. Additional feedback includes the DC-bus voltage as well as the PWM filtered three phase voltages to allow validation of advanced sensorless designs like InstaSPIN-FOC.

The three-phase inverter operates from a wide input voltage range 12V to 60V and offers onboard power management that provides a 5V rail to supply the LMG2100 gate driver and 3.3V band-gap reference well a 3.3V rail for the INA241 current sense amplifiers and temperature switch.

The TIDA-010936 offers a TI BoosterPack compatible 3.3V I/O interface to connect to a C2000 MCU LaunchPad development kit for quick and easy performance evaluation.