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

1 System Description

Many end equipment require user-provided position information to properly function. From a user’s perspective, the inputs can be provided by various methods, such as pressing a button, pressing a trigger, or turning a knob. A mechanism is often needed to translate the inputs from the user to a form that can be sensed and then acted on by the electronics within the system. As an example, cordless power tools like power drills require a mechanism to translate the trigger displacement into a voltage that controls the speed of the tool. Potentiometers are commonly used for translating how far the user presses the trigger into an output voltage, however, this type of mechanical implementation has issues with wear and tear that reduce product lifetime.

To reduce current consumption, cordless power drills are also put in a low-power mode to prevent from draining the battery of the tool. Pressing the trigger wakes up the power drill. Mechanical implementations such as mechanical switches may be used to wake up the system once the trigger displacement exceeds a minimum threshold distance. Mechanical switches also have issues with wear and tear, similar to potentiometers.

In this reference design, a contactless trigger is implemented using Hall-effect sensors, which reduces wear and tear compared to traditional triggers that use potentiometers and mechanical switches. This design includes a 3D-printed trigger module with embedded magnet for illustrating a Hall-based trigger press mechanism. In this implementation, a magnet is placed so that it moves along with the trigger. As the trigger is pressed, the magnet approaches a linear Hall sensor, which translates the sensed magnetic flux density from the moving magnet into an output voltage. Since the sensed magnetic flux density and output voltage varies with the location between the magnet and the linear Hall sensor, the output voltage provides information on the location of the magnet, and therefore, the trigger displacement. This design translates up to 10 mm of trigger displacement into an output voltage.

A load switch is used to disconnect power to the linear Hall sensor and other components if the trigger is not pressed. To wake up the system to enter active mode, the design utilizes a Hall-effect switch for detecting when the trigger displacement exceeds the turn-on distance. When the sensed magnetic flux density of the wake-up Hall-effect switch exceeds the magnetic operating point (BOP) of the switch, the output of the Hall-effect switch is asserted low, which triggers the load switch to reconnect power to the linear Hall sensor.

In addition to the wake-up Hall-effect switch, additional Hall-effect switches are present for implementing optional protection against external magnetic fields. If these additional Hall-effect switches detect strong external magnetic fields, the output of the linear Hall-sensor is disabled by disconnecting power to it, thereby preventing the power drill from accidentally turning ON due to strong external magnetic fields tampering with the system. This protection also turns OFF a currently ON drill when strong magnetic fields are present. Each of the tamper Hall sensors can be individually disabled, which enables the user to select the number of Hall sensors needed for their system based on their sleep current consumption, and external magnetic field protection requirements.

This design supports standalone operation or connection to external systems for in-system evaluation. In standalone operation, the design is powered from AAA batteries that are inserted into the battery holder that comes with the HALL-TRIGGER-EVM. To illustrate status, the following LEDs are used:

  • LEDs on the output of each Hall-effect switch
  • An LED added to the VCC input of the linear Hall sensor for indicating system wake up from its sleep mode and when the linear Hall sensor is powered
  • An LED that changes its brightness based on how far the trigger is pressed

For connecting to external systems for in-system evaluation, an LDO is included in the design to convert external battery voltages from 5 V to 30 V down to a 3.3-V rail that powers the design. Instead of connecting the DRV5056 power to the load switch output, the design can also be reconfigured so that the DRV5056 is powered from an external 3.3-V rail. In addition, an optional BJT circuit on the design is present (this is not populated by default) to translate the internally generated 3.3-V system wake-up signal to a voltage set to the voltage of the external battery.

In addition to being applicable to cordless power tools, this design is also applicable for other end equipment that have a trigger mechanism, such as surgical equipment, mains powered tools, and food blenders.