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

2.2.3 Power Tree Architecture

Historically, these respiratory applications have used isolated AC/DC power bricks to provide 12 V, 19 V, or 24 V DC bus voltages to the system. The system then either uses the higher DC bus voltage to drive the motors and valves directly, or they step down the voltage through a buck converter. However, as the market for many of these systems move towards portability, they will have to be operated off of battery voltages which are estimated to range from 6-14 V. Given this shift, the reference design has a defined input voltage range of 6-28 V. Additionally, the transition to portability means that the key system requirements include high efficiency to allow longer battery lifetimes. Generally, solution size also has a higher priority for these systems, which was considered in this reference design.

The DRV8323RS is capable of operating under the full voltage range, so the DRV8323RS and BLDC motor has been tied directly to the input voltage source. However, solenoid valves need to operate at a single DC voltage, so a stable 12 V DC voltage was selected as a required rail. Given that 12 V falls in the middle of the input voltage range a buck-boost or SEPIC topology converter would be the optimal choice to generate the 12 V DC rail. However, with the understanding that some manufacturers will only need a buck converter (for regulated DC inputs) or a boost converter (for battery inputs), separate buck and boost converters were selected to work in sequence to generate the 12 V rail.

The LM5122 wide input synchronous boost controller was selected as the first stage of the power tree after the input. The device was configured to boost to 14 V to cover the battery voltage range and was also selected to get the highest efficiency as a synchronous controller offers the opportunity to select both switching MOSFETs. Additionally, this device has the unique feature of an external charge-pump that can drive the high-side MOSFET when the input voltage goes higher than the set output voltage. This mode is called pass-through and allows power to be efficiently delivered through the high-side MOSFET without changing the input voltage. It is also useful to note that the device operates in peak current-mode control for fast transient response. The LMR33630 is a 3 A synchronous buck converter that was selected due to its small size and high efficiency. The device has been configured to step down to 12 V from the possible input range of 14-28 V, covering the rest of the input voltage range. Placement was optimized in the design for these two devices to showcase their individual solution sizes.