SLIA096 January   2022 DRV5021 , DRV5021-Q1 , DRV5023 , DRV5023-Q1 , DRV5032 , DRV5033 , DRV5033-Q1 , TMAG5123 , TMAG5123-Q1 , TMAG5124 , TMAG5124-Q1 , TMAG5231 , TMAG5328

 

  1.   Trademarks
  2. 1Introduction
  3. 2Design Process
    1. 2.1 Mechanical Implementation
    2. 2.2 Magnetic Implementation
    3. 2.3 Magnet Sensor Placement
    4. 2.4 Prototyping and Bench Testing
    5. 2.5 Layout
    6. 2.6 Bench Testing
    7. 2.7 Bench Results
    8. 2.8 Error Sources
      1. 2.8.1 Offsets
      2. 2.8.2 Roll, Yaw, and Pitch
      3. 2.8.3 Magnet Variation
      4. 2.8.4 Device Variation and Temperature Drift
      5. 2.8.5 External Fields
      6. 2.8.6 Nearby Material Influence
      7. 2.8.7 Bench Setup Error
  4. 3Summary

Offsets

Offset corresponds to the displacement between the magnet and Hall-effect device, when the mechanical switch is oriented at the 0° angle. Figure 2-23 illustrates how offsets are defined in the calculator tool.

Figure 2-23 Displacement Offsets

The source of offset error can be attributed to PCB manufacturing and rocker assembly manufacturing. In the example documented in this note, while the PCBs were fabricated by a PCB manufacturer, the slots for the holding rocker were hand drilled. The rocker assembly was 3D printed, and the printer has a resolution of 0.0125 to 0.05 mm. Due to the level of precision when cutting the slots, there were notable instances in which the assemblies were a little off center and their bases not flush with the board. In addition to these manufacturing and assembly errors, there was also a z-offset error contributed by the tool. The tool assumes all SOT-23 packages are 1.12-mm tall and uses that value for calculating the surface to Hall-element offset. Post analysis revealed that some package heights were as low as 0.947 mm.

Large tolerances in the x-offset, y-offset, sensor z-offset, and magnet z-offset can all have a significant impact on the B-field detected at the DUT Hall element, especially when the magnet size is small. Figure 2-24 and Figure 2-25 show how much the BOP maximum angle can change with respect to the offset from our ideal magnet position.

GUID-20211229-SS0I-NCZX-JSPF-DMMZS4CPTLS7-low.png Figure 2-24 X and Y Offset Impact on BOP Max Angle
GUID-20211229-SS0I-3R2H-FR6H-FCSK52FP3TQS-low.png Figure 2-25 Z Offset on BOP Max Angle