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
2.3.1.2.2 DRV5056 Output Voltage

The DRV5056 in this design senses the magnetic flux density produced by the trigger magnet and translates this sensed magnetic flux density into voltage using :

Equation 1. VDRV,OUT = B × S + VQ

where

  • B is the sensed magnetic flux density
  • S is the sensitivity of the selected DRV5056 variant (the DRV5056A1 in this design has a typical sensitivity of 120 mV/mT at 3.3 V)
  • VQ is the quiescent voltage (0.6 V typical).

Note that the maximum recommended current that can be drawn from the DRV5056 voltage output pin is ±1 mA, so any circuit connected to the DRV5056 output must be designed to ensure that it does not draw more than ±1 mA from the DRV5056 OUT pin.

In this design, the D6 TRIG LED increases its brightness as the trigger is pressed. The brightness is adjusted by using a TLV9061 op-amp circuit. Resistors R6, R7, R8, and R10 were selected to translate the DRV5056 output voltage into a voltage that could drive the cathode of the LED so that the trigger magnet movement changes the intensity of this LED. The anode of D6 is connected to VCC_2, which is the switched voltage rail from the output of the TPS22917. The voltage applied to the cathode of D6 is approximately equal to (0.728 × VCC_2) – (VDRV,OUT × 0.699). As a result, the voltage across the diode will be approximately (0.272 × VCC_2) + (VDRV,OUT × 0.699). The LED turns ON when the voltage across it is greater than 1.7 V. As the trigger is pressed, the voltage drop across the LED increases, thereby increasing the brightness of the LED. In addition to selecting the resistors to obtain the desired cathode voltage, these resistor values were selected so that they do not draw more than ±1 mA from the DRV5056 output. By performing circuit simulation on this circuit, it was verified that this circuit takes less than ±50 μA of current from the DRV5056 OUT pin.

The TLV9061 circuit is used to drive the D6 LED for demonstration purposes when in standalone mode. It is possible to connect the DRV5056 output to an external system by removing resistor R5 so that the DRV5056 output is isolated from the TLV9061 circuit. If it is desired to divide the output from the DRV5056, resistors R10 (currently 51.1 kΩ) and R11(currently DNP) can be replaced with values that divide the DRV5056 as needed. The output voltage from this resistor divider is brought out to the “DIV” test point on the board.