JAJU835 December   2021

 

  1.   概要
  2.   リソース
  3.   特長
  4.   アプリケーション
  5.   5
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
      1.      10
    2. 2.2 Highlighted Products
      1. 2.2.1 DRV5056
      2. 2.2.2 DRV5032
      3. 2.2.3 TPS709
      4. 2.2.4 SN74HCS00
      5. 2.2.5 TPS22917
      6. 2.2.6 SN74AUP1G00
      7. 2.2.7 TLV9061
    3. 2.3 Design Considerations
      1. 2.3.1 Design Hardware Implementation
        1. 2.3.1.1 Hall-Effect Switches
          1. 2.3.1.1.1 U1 Wake-Up Sensor Configuration
          2. 2.3.1.1.2 U2 Stray-Field Sensor Configuration
          3. 2.3.1.1.3 U3 and U4 Tamper Sensor Configuration
          4. 2.3.1.1.4 Hall Switch Placement
            1. 2.3.1.1.4.1 Placement of U1 and U2 Sensors
              1. 2.3.1.1.4.1.1 U1 and U2 Magnetic Flux Density Estimation Results
            2. 2.3.1.1.4.2 Placement of U3 and U4 Hall Switches
              1. 2.3.1.1.4.2.1 U3 and U4 Magnetic Flux Density Estimation Results
          5. 2.3.1.1.5 Using Logic Gates to Combine Outputs from Hall-Effect Switches
        2. 2.3.1.2 Linear Hall-Effect Sensor Output
          1. 2.3.1.2.1 DRV5056 Power
          2. 2.3.1.2.2 DRV5056 Output Voltage
          3. 2.3.1.2.3 DRV5056 Placement
        3. 2.3.1.3 Power Supply
        4. 2.3.1.4 Transistor Circuit for Creating High-Voltage Enable Signal
      2. 2.3.2 Alternative Implementations
        1. 2.3.2.1 Replacing 20-Hz Tamper Switches With 5-Hz Tamper Switches
        2. 2.3.2.2 Using Shielding to Replace Tamper Switches and Stray Field Switch
        3. 2.3.2.3 Replacing Hall-Based Wake-Up Alert Function With a Mechanical Switch
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
      1. 3.1.1 Installation and Demonstration Instructions
      2. 3.1.2 Test Points and LEDs
      3. 3.1.3 Configuration Options
        1. 3.1.3.1 Disabling Hall-Effect Switches
        2. 3.1.3.2 Configuring Hardware for Standalone Mode or Connection to External Systems
    2. 3.2 Test Setup
      1. 3.2.1 Output Voltage Accuracy Testing
      2. 3.2.2 Magnetic Tampering Testing
      3. 3.2.3 Current Consumption Testing
    3. 3.3 Test Results
      1. 3.3.1 Output Voltage Accuracy Pre-Calibration Results
      2. 3.3.2 Output Voltage Accuracy Post-Calibration Results
      3. 3.3.3 Magnetic Tampering Results
      4. 3.3.4 Current Consumption Results
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Tools and Software
    3. 4.3 Documentation Support
    4. 4.4 サポート・リソース
    5. 4.5 Trademarks

2.2.1 DRV5056

The DRV5056 is a linear Hall-effect sensor that responds proportionally to positive magnetic flux density readings. The device uses a ratiometric architecture that can reduce error from VCC tolerance when the external analog-to-digital converter (ADC) uses the same VCC for its reference. The DRV5056 is sensitive to the magnetic field component that is perpendicular to the die inside the package. Figure 2-3 shows the direction of sensitivity for the DRV5056.

GUID-D1C79E32-9A03-46A3-A01C-6219292394D6-low.gifFigure 2-3 DRV5056 Direction of Sensitivity

This design uses the TO-92 through-hole package. For the TO-92 package of this device, a positive magnetic flux density is defined as when the magnetic south pole applied near the front (marked) of the package or a north pole applied from behind the package. Figure 2-4 shows the magnetic response of the device. This device is a unipolar device, where the analog output drives 0.6 V when no magnetic field is present and increases as the positive field becomes stronger.

GUID-F7E24FC2-A197-4AA4-B718-88705A16F13E-low.gifFigure 2-4 DRV5056 Magnetic Response

The bipolar DRV5055 can be used an alternative to the DRV5056. The DRV5055 responds to both positive and negative fields instead of just negative fields. The advantage of the DRV5055 is that it can still work if the magnet was accidentally installed backwards since the device senses both negative and positive fields (note that the wake-up and stray field sensors will not work if the magnets are reversed because they are unipolar as well). For the head-on configuration used in this design, the linear Hall sensor is only exposed to either a positive field or a negative field during the trigger movement; it is not exposed to both fields when the trigger is pressed. For more information, see the Head-on Linear Displacement Sensing Using Hall-Effect Sensors application brief. As a result, only half the range of the DRV5055 is used if the DRV5055 is used as the linear Hall sensor for the design. Since the DRV5056 is a unipolar device; however, the entire range of the DRV5056 can be used. To maximize output dynamic range, the DRV5056 was selected in this design instead of the DRV5055.

The DRV5056A1 device variant was selected in this design because its magnetic range (20 mT) is near the maximum magnetic flux density that is expected to be detected by the DRV5056 based on the magnet material, magnet dimensions, and the distance from the magnet to the DRV5056 sensing element.