TIDUBY9 December   2021

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  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 Support Resources
    5. 4.5 Trademarks
2.3.1.1.4.2 Placement of U3 and U4 Hall Switches

The following procedure was used to find the placement of U3 and U4:

  1. An initial z-component displacement of 0 mm was selected for the z-component distance from the sensing element of switch U1 to the sensing element of switch U3. The same displacement was selected for the distance from the sensing element of switch U1 to the sensing element of switch U4.
  2. An initial x-component displacement was selected for the distance from the dot on the magnet to U3. Since U3 and U4 cannot be moved in the x direction due to being surface mount parts with fixed heights, there are only two options where U3 and U4 can be placed: on the top layer or bottom layer of the PCB. Due to the placement of the PCB within the 3D printed trigger module, the shortest distance from U1 and U2 to an external magnet is when the magnet is applied underneath the trigger module as shown in Figure 2-11 and Figure 2-12. Consequently, U1 and U2 in this design are more affected by external magnets applied underneath the PCB and trigger module. To deal with the susceptibility of U1 and U2 to magnets applied underneath the trigger module, tamper Hall switches U3 and U4 were placed at the bottom layer of the PCB to more closely detect external magnets applied underneath the trigger module. Outside of changing the PCB layer U3 and U4 are placed on, the x-component displacement can also be changed by moving the magnet in the x direction. If the magnet is moved in the x direction, note that the impact of this change on the DRV5056 output must be verified if the height of the DRV5056 through-hole package cannot be adjusted accordingly.
  3. An initial y-component displacement was selected for the y-component distance from the sensing element of switch U1 to the sensing element of switch U3. This displacement should be far away from the trigger magnet so that it does not detect the trigger movement as an external magnetic field, but it should also be close enough to the wake-up sensor to detect nearby external magnetic fields affecting U1. Figure 2-17 shows a picture of the back of the trigger module, where the back surface is removed so that the bottom of the PCB is visible. The rectangle with the “+” in it is a projection of switch 1 from its actual position on the top of the PCB to the bottom layer of the PCB that is shown in Figure 2-17. The footprint of U1 is projected onto the figure to show the y and z displacements of U1 to U2 and U3.
    GUID-20211214-SS0I-VMFT-8B46-T1JXSGPMPC9M-low.pngFigure 2-17 Placement of U3 and U4 Sensors
  4. After the y component of U3 was selected, a simulation was done to verify that the sensed magnetic flux density of the sensor was less than BOP during the entire trigger displacement range. Additionally, the sensed magnetic flux density should be less than BRP when the trigger is at rest so that the tamper outputs of the Hall sensor are automatically cleared when the trigger goes back to its rest position. If these conditions are not met, take the following actions:
    1. Restart from step 3 with a different y-component displacement.
    2. Restart from step 2 with a different x-component displacement. Note that the impact of this change on the DRV5056 output must be verified if the height of the DRV5056 through-hole package cannot be adjusted accordingly.
    3. Modify the dimensions or material of the magnet and restart from step 2. Note that the impact of this change on the DRV5056 output must be verified.
  5. Repeat steps 3 and 4 but for U4 instead of U3.

Based on implementing the previous procedures, the following distances were obtained and used for this design:

  • U3 distance components
    • X-component displacements
      • X-component from bottom of package to white dot of magnet = 9.40 mm
      • X-component from bottom of package to bottom of magnet = 9.40 – magnet radius = 7.02 mm
      • X-component (sensor z-offset in tool) from sensing element to bottom of magnet to sensing element = 7.02 + 0.650 = 7.67 mm
    • Y-component displacement = +10 mm.
    • Z-component displacement (same as U1)
      • Trigger not pressed
        • Z-component from sensing element to white dot of magnet = 2.18 mm
        • Z-component from sensing element to magnet center = 2.18 – 0.5 × magnet thickness = 2.18 – 0.5(4.76) = –0.2 mm
      • Maximum trigger displacement = 10 mm
        • Z-component from sensing element to white dot of = 12.18 mm
        • Z-component from sensing element to magnet = 12.18 – 0.5 × magnet thickness) = 12.18 – 0.5(4.76) = 9.8 mm

  • U4 distance components

    • X-component displacements
      • X-component from bottom of package to white dot of magnet = 9.40 mm
      • X-component from bottom of package to bottom of magnet = 9.40 – magnet radius = 7.02 mm
      • X-component (sensor z-offset in tool) from sensing element to bottom of magnet to sensing element = 7.02 + 0.650 = 7.67 mm
    • Y-component displacement = –10 mm.
    • Z-component displacement (same as U1)
      • Trigger not pressed
        • Z-component from sensing element to white dot of magnet = 2.18 mm
        • Z-component from sensing element to magnet center = 2.18 – 0.5 × magnet thickness = 2.18 – 0.5(4.76) = –0.2 mm

      • Maximum trigger displacement = 10 mm

        • Z-component from sensing element to white dot of = 12.18 mm
        • Z-component from sensing element to magnet = 12.18 – 0.5 × magnet thickness) = 12.18 – 0.5(4.76) = 9.8 mm