TIDUCL0 January   2017

 

  1. 1 Description
  2. 2 Resources
  3. 3 Features
  4. 4 Applications
  5. 5 Design Images
  6. 6 System Overview
    1. 6.1 System Description
    2. 6.2 Key System Specifications
    3. 6.3 Block Diagram
    4. 6.4 Highlighted Products
      1. 6.4.1 CSD88584Q5DC
      2. 6.4.2 DRV8323
      3. 6.4.3 MSP430F5132
      4. 6.4.4 TPS54061
      5. 6.4.5 LMT87
  7. 7 System Design Theory
    1. 7.1 Power Stage Design—Battery Power Input to the Board
    2. 7.2 Power Stage Design—Three-Phase Inverter
      1. 7.2.1 Design Considerations in Paralleling MOSFETs
        1. 7.2.1.1 Conduction Phase
        2. 7.2.1.2 Switching Phase
      2. 7.2.2 Selecting the Sense Resistor
    3. 7.3 Power Stage Design—DRV8323 Gate Driver
      1. 7.3.1 Gate Drive Features of DRV8323
      2. 7.3.2 Current Shunt Amplifier in DRV8323
      3. 7.3.3 Protection Features in DRV8323
    4. 7.4 Power Stage Design—18-V to 3.3-V DC-DC Converter
    5. 7.5 Power Stage Design —Microcontroller MSP430
    6. 7.6 Power Stage Design—Hall Sensor Interface
    7. 7.7 Temperature Sensing
    8. 7.8 Power Stage Design—External Interface Options and Indications
      1. 7.8.1 Speed Control of Motor
      2. 7.8.2 Direction of Rotation—Digital Input
      3. 7.8.3 LED Indications
      4. 7.8.4 Signal Interface Connector for External Monitoring and Control
  8. 8 Getting Started Hardware and Software
    1. 8.1 Hardware
      1. 8.1.1 Connector Configuration of TIDA-00774
      2. 8.1.2 Programming of MSP430
      3. 8.1.3 Procedure for Board Bring-up and Testing
    2. 8.2 Software
      1. 8.2.1 System Features
      2. 8.2.2 Customizing the Reference Code
        1. 8.2.2.1 PWM_PERIOD
        2. 8.2.2.2 MAX_DUTYCYCLE
        3. 8.2.2.3 MIN_DUTYCYCLE
        4. 8.2.2.4 ACCEL_RATE
        5. 8.2.2.5 Block_Rotor_Duration
      3. 8.2.3 Configuring the DRV8323 Registers (drv8323.c)
      4. 8.2.4 Initializing SPI Communication Between DRV8323 and MSP430 (drv8323.h)
      5. 8.2.5 Running Project in Code Composer Studio (CCS)
  9. 9 Testing and Results
    1. 9.1 Test Setup
    2. 9.2 Test Data
      1. 9.2.1 Functional Tests
        1. 9.2.1.1 3.3-V Power Supply Generated by Step-Down Converter
        2. 9.2.1.2 Gate Drive Voltage Generated by Gate Driver
        3. 9.2.1.3 Dead Time From DRV8323
        4. 9.2.1.4 MOSFET Switching Waveforms
        5. 9.2.1.5 VGS Skew of Parallel FETs During Switching
      2. 9.2.2 Load Test
        1. 9.2.2.1 Load Test Without Heat Sink
        2. 9.2.2.2 Load Test With Heat Sink
        3. 9.2.2.3 Load Test With Heat Sink and Airflow
      3. 9.2.3 Inverter Efficiency Test
      4. 9.2.4 Thermal Rise at Different Power Levels
      5. 9.2.5 Inverter Current Sensing by VDS Monitoring
      6. 9.2.6 Overcurrent and Short-Circuit Protection Test
        1. 9.2.6.1 Cycle-by-Cycle Stall Current Protection by DRV8323 VDS Sensing
        2. 9.2.6.2 Stall Current Latch Protection by DRV8323 VDS Sensing
      7. 9.2.7 Testing for Peak Current Capability
  10. 10Design Files
    1. 10.1 Schematics
    2. 10.2 Bill of Materials
    3. 10.3 PCB Layout Recommendations
      1. 10.3.1 Layout Prints
    4. 10.4 Altium Project
    5. 10.5 Gerber Files
    6. 10.6 Assembly Drawings
  11. 11Software Files
  12. 12Related Documentation
    1. 12.1 Trademarks
  13. 13Terminology
  14. 14About the Author

9.2.6.1 Cycle-by-Cycle Stall Current Protection by DRV8323 VDS Sensing

Figure 45 shows the test setup to simulate a stall current when the motor is rotating. S1 is a single-throw, double-pole switch connected between the motor terminals. This is used to create a motor winding to winding short.

Before S1 is closed, the motor was rotating at a steady speed. Figure 46 shows the waveforms obtained when the switch S1 is closed. When S1 is closed, S1 carries the short-circuit current. During this condition the motor stops, which causes the Hall state to continue at the current commutation state; therefore, the controller continues to generate the PWM corresponding to this commutation state.

The VDS reference for stall current limit is set to 0.1 V.

TIDA-00774 tida-00774-test-setup-to-simulate-stall-current-when-motor-is-running.gifFigure 45. Test Setup to Simulate Stall Current When Motor is Running

With the VDS reference of 0.1 V and considering a 1-mΩ RDS_ON / FET and with two FETs in parallel, set current limit = 0.1 / 0.0005 = 200 A

Figure 47 shows a zoomed view of Figure 46, the cycle-by-cycle overcurrent protection acted at around 178 A. Once the current hits 178 A, the PWM shuts off immediately, and the response time is less than 1 µs.

TIDA-00774 tida-00774-cycle-by-cycle-overcurrent-protection-with-motor.pngFigure 46. Cycle-by-Cycle Overcurrent Protection With Motor Stall
TIDA-00774 tida-00774-cycle-by-cycle-overcurrent-protection-with-motor-zoomed.pngFigure 47. Zoomed View of Cycle-by-Cycle Overcurrent Protection With Motor Stall

Figure 48 shows the test setup to simulate a short circuit at the inverter output.

TIDA-00774 tida-00774-test-setup-to-simulate-inverter-short-circuit.gifFigure 48. Test Setup to Simulate Inverter Short Circuit

The VDS reference for short circuit is set to 0.1 V. Figure 49 shows the overcurrent protection acted at around 186 A. Once the current hits 186 A, the PWM shuts off immediately and the response time is less than 1 µs.

TIDA-00774 tida-00774-cycle-by-cycle-overcurrent-protection-with-inverter-output-shorted.pngFigure 49. Cycle-by-cycle Overcurrent Protection With Inverter Output Shorted