JAJU873 August   2020

 

  1.   概要
  2.   リソース
  3.   特長
  4.   アプリケーション
  5.   5
  6. 1 System Description
    1. 1.1 Medical Respiratory Systems
    2. 1.2 Respirator System Components
    3. 1.3 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Brushless DC Motor (BLDC)
        1. 2.2.1.1 DRV8323RS BLDC Motor Driver Design Calculations
        2. 2.2.1.2 BLDC Motor Driver Circuit
      2. 2.2.2 Solenoid Valve Drivers
        1. 2.2.2.1 DRV8847 Solenoid Driver Design Calculations
        2. 2.2.2.2 Solenoid Driver Circuit
      3. 2.2.3 Power Tree Architecture
        1. 2.2.3.1 Input protection - overvoltage and reverse voltage
        2. 2.2.3.2 LM5122 Boost Design Calculations
        3. 2.2.3.3 LMR33630 Buck Design Calculations
        4. 2.2.3.4 Secondary Power Stage – TPS62840 3.3V Buck
        5. 2.2.3.5 Secondary Power Stage – TPS7A02 3.3V LDO
        6. 2.2.3.6 Power Tree Circuit
    3. 2.3 Highlighted Products
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware and Software Requirements
    2. 3.2 Test Setup
      1. 3.2.1 Hardware Configuration
      2. 3.2.2 Software Configuration
    3. 3.3 Test Results
      1. 3.3.1 Motor Test Result
      2. 3.3.2 Valve Test Result
      3. 3.3.3 Power Tree Test Result
      4. 3.3.4 Key Test Summary
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Documentation Support
    3. 4.3 サポート・リソース
    4. 4.4 Trademarks
  10. 5About the Author

2.2.1 Brushless DC Motor (BLDC)

Pressurized air for these applications can be generated using several motor types including brushed-DC (BDC), BLDC, and even AC motors. Of the three types mentioned, AC motors are the easiest to control. However, AC motors use additional energy to create the electromagnet, which decreases their efficiency, and they tend to be physically larger than both BDC and BLDC motors. AC motors also do not have capability to change speed quickly. BDC motors tend to have a lower cost and simpler control schemes than BLDC motors. However, BLDC motors offer several advantages that make them especially desirable for respiratory medical applications. The largest benefit of these motors is that they lack the brushes and are contactless, which means that they are inherently much quieter than BDC motors and will have a longer lifetime. Brushed-DC motors will wear out more quickly due to the brushes degrading over time. Additionally, while the control can be far more complex for BLDC motors, BLDC motors are the most efficient motor type and smallest in size for a given motor power. Brushless-DC motors are also capable of the highest speed and best dynamic speed performance (acceleration and deceleration) compared to other motor types.

To achieve the quietest and most efficient operation, field-oriented control (FOC) is often used as a control algorithm. FOC is a technology that applies all torque on the motor perpendicular to the rotor; this allows for maximum drive effectiveness. Additionally, many systems implement a sensorless control scheme, meaning that there are no Hall-Effect sensors embedded on the motor itself. Sensorless drive schemes allow a wider range of motors to be used, however sensored drive systems may also be implemented if the motor used has sensors built in. TI features a technology called InstaSpin-FOC, which runs on select Piccolo series MCU and can be a quicker way to bring up sensorless FOC compared to designing the control scheme from the ground up.

The DRV8323RS was selected as the motor gate driver for this design based on several features. For example, the DRV8323RS has three integrated half-bridge drivers capable of sourcing 2 A and sinking 1 A to the MOSFET gates. It also integrates the charge pump for the high side MOSFETs for 100% duty cycle, an asynchronous buck converter capable of supporting up to 600 mA for external use, and three low-side current sense amplifiers to sense the motor current. Another important aspect in the selection of this device is that it is capable of handling the entire voltage range desired for this reference design, 6-28 V.

To achieve the desired FOC algorithm, the latest Piccolo MCU, TMS320F28027F, has been selected to run TI’s InstaSpin-FOC control software. The reference design includes connectors to attach to the Piccolo’s Launchpad. In this way, FOC is integrated into the design through a plug-and-play peripheral to allow users to easily test this control algorithm.