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

2.2.2.1 DRV8847 Solenoid Driver Design Calculations

The DRV8847 device is configured for independent half-bridge operation. Mode selection is done using the I2C registers in the DRV8847S device variant. Refer to the data sheet for more details. The solenoid driver design is summarized below:

Table 2-2 Solenoid Driver Design Summary
PARAMETER SPECIFICATION
Solenoid operating voltage 12 V
Unidirectional solenoid drive 4 Channels
Bidirectional solenoid drive 2 Channels
Solenoid drive current 4x 0.5 A (unidirectional), 2x 0.5 A (bidirectional)
Max valve response time 1 ms
Operation temperature range 5-40 °C

Based on the data sheet, the DRV8847 integrated FET max RDS(on) is 700 mΩ (VM = 12 V; IOUT = 0.5 A; TA = 85 °C). For unidirectional drive, each channel conduction loss is:

Equation 35. GUID-20200804-CA0I-Z44L-MFGB-LW1K6QRRJTZK-low.gif

For four active channels, the total conduction loss is 700 mW. The junction temperature is calculated as follows:

Equation 36. GUID-20200804-CA0I-TVCW-FLLQ-B0D1MPX09VXS-low.gif

For bidirectional drive, each channel conduction loss is

Equation 37. GUID-20200804-CA0I-BMVH-QJ5H-K9SVXC7JMHR6-low.gif

For two active channels, the total conduction loss is 700 mW. The junction temperature is calculated as follows:

Equation 38. GUID-20200804-CA0I-KMNV-FBLM-DN1RFFMXXH1V-low.gif

This junction temperature allows some margin for other sources of power dissipation and design tolerances.

The switching frequency for solenoid is expected to be relatively low (e.g. 200 Hz), thus the switching loss is negligible:

Equation 39. GUID-20200804-CA0I-4PT4-JHVN-BF4VJV0TV2FJ-low.gif