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

6.1 System Description

Power tools are used in various industrial and household applications such as drilling, grinding, cutting, polishing, driving fasteners, various garden tools, and so on. The most common types of power tools use electric motors while some use internal combustion engines, steam engines, or compressed air. Power tools can be either corded or cordless (battery powered). Corded power tools use the mains power (the grid power) to power up the AC or DC motors. The cordless tools use battery power to drive DC motors.

Most of the cordless tools use lithium-ion batteries, the most advanced in the industry. Lithium-ion batteries have high energy density, low weight, and greater life. These batteries have relatively low self-discharge (less than half that of nickel-based batteries) and can provide a very high current for applications like power tools.

Power tools are available in different power levels and battery voltage levels. Power tools such as cordless chain saws and cordless circular saws and different garden tools like cordless wood and branch cutters require very high torque and need very high peak current.

Cordless tools use brushed or brushless DC (BLDC) motors. The BLDC motors are more efficient and have less maintenance, low noise, and longer life. Power tools have requirements on form factor and thermal performance. Therefore, high-efficient power stages with a compact size are required to drive the power tool motor. The small form factor of the power stage enables flexible mounting, better PCB layout performance, and low-cost design. High efficiency provides maximum battery duration and reduces cooling efforts. The high-efficiency requirement in turn asks for switching devices with a low drain-to-source resistance (RDS_ON). The power stage should also take care of protections like motor stall or any other chances of high current.

This TI Design uses the CSD88584 NexFET power block featuring a very low RDS_ON of 1 mΩ in a SON5×6 SMD package. The power block with high-side and low-side FETs in single package helps to achieve very small form factor and better switching performance. The three-phase gate driver DRV8323 is used to drive the three-phase MOSFET bridge, which can operate from 6 to 60 V and support programmable gate current with maximum setting of 2-A sink / 1-A source. The DRV8323 includes three current shunt amplifiers, which helps in measuring and amplifying the VDS of the FET for accurate current measurements that support bidirectional current sensing with adjustable gain and eliminates the use of shunt. The SPI provides detailed fault reporting and flexible parameter settings such as gain options for the current shunt amplifier, slew rate control of the gate drivers, and various protection features.

The LMT87 temperature sensor is used to sense the FET temperature and the results is used to calibrate the current sensing by VDS monitoring. The MSP430F5132 microcontroller is used to implement the control algorithm.

The test report evaluates the RMS current capability, peak current capability, and thermal performance of the board and overcurrent protection features such as cycle-by-cycle control and latch control of the DRV8323. The test results also show the improved RMS current capability of the board with different air flow.