SLYA092 June   2025 TMAG3001

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Z-Axis Pressing Offset Issue in 3D Linear Hall Sensor
    1. 2.1 Root Cause of X, Y Offsets in Z-axis Pressing Action
  6. 3The Z-Axis Pressing Detection Method
    1. 3.1 General Introduction of Proposed Method
    2. 3.2 Software Slew Rate Detection
    3. 3.3 Hardware Threshold Detection and Interrupt
    4. 3.4 Latching Method
      1. 3.4.1 Implementation of Two-Level Detection Method
    5. 3.5 Test Result
  7. 4Summary
  8. 5References

2.1 Root Cause of X, Y Offsets in Z-axis Pressing Action

Figure 2-1 shows the designed for behavior during the pressing action of the Z-axis.

  • No mechanical error between the center point of 3D linear Hall Sensor and joystick.
  • The pressing action always keeps vertical angle

Please note that the Hall elements inside 3D linear Hall-effect sensor are not at the midpoint of TMAG3001. This requires a small offset from package center to properly align the device.

Through TI Magnetic Sense Simulator (TIMSS) simulations, the expected magnetic field can be modeled and used to perform calculations. If the magnet moves downwards, the magnetic flux in either the X and Y direction does not change and the magnetic flux in Z axis can increase exponentially. This model was then reproduced using the TMAG3001EVM and GUI, we can directly observe that the magnetic change is inversely proportional to r2.

TIMSS Simulation ModelFigure 2-1 TIMSS Simulation Model
Table 2-1 Simulation Results When Moving Magnet in Z-axis
Z_axis Displacement(mm)Bx(mT)By(mT)Bz(mT)
00025.12599
0.250029.55061
0.50035.07820
0.750042.07500
10051.06340

In non-ideal situation, there are two main reasons either X or Y offsets can be observed from the sensor

  • Mechanical error between joystick and 3D linear Hall sensor
  • Manual press cannot be completely perpendicular to the sensor

The mechanical error indicates that the 3D linear Hall sensor can have a certain level of deviation compared to the reference value, as shown in Figure 2-2. While this is designed for to target the center of the sensing element, manufacturing tolerances during soldering and product assembly can inevitably cause some potential design errors.

More importantly, the joystick can tilt somewhat during the pressing action caused by imperfect user control. This mechanical error causes the sensor to no longer reside where the magnetic field vector is entirely contained within the Z-axis, and some component can be observed in either the X or Y axes. As a result, this is not uncommon to observe a small deviation with offset to either the X or Y axes.

Mechanical Error Between Magnet and Hall SensorFigure 2-2 Mechanical Error Between Magnet and Hall Sensor