SLYA065 October   2022 TMAG5328

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
    1. 1.1 Mapping Switching Distance to Magnetic Flux Density
    2. 1.2 How to Program BOP of TMAG5328
    3. 1.3 Advantages of TMAG5328 Adjustable BOP
  4. 2Determining Sensed Magnetic Flux Density Seen by TMAG5328
  5. 3Implementing a Software-Programmable Hall-Effect Switch With Microcontroller-Less Standalone Mode
  6. 4Implementing Diagnostics and a Magnetic Window Comparator
    1. 4.1 Conducting Diagnostic Tests With TMAG5328EVM and Head-On Linear Displacement 3D Print
      1. 4.1.1 Magnet Out-of-Range Testing (Magnetic Window Comparator Testing)
        1. 4.1.1.1 Signal Disconnections
        2. 4.1.1.2 Signal Shorts
  7. 5Summary

1.1 Mapping Switching Distance to Magnetic Flux Density

The relationship between the sensed magnetic flux density and the magnet-to-sensor distance along with the BOP and BRP determine the magnet-to-sensor distance at which the switch changes state. In many cases, the magnet travels in a direct linear path of travel, so distance is often expressed by the direct magnet-to-sensor distance. In Figure 1-1, however, distance is specified by the angle of opening because the refrigerator door opens on a hinge that causes the magnet to move nonlinearly. For Figure 1-1, the magnet-to-sensor distance increases as the angle of opening increases.

Figure 1-3 shows an example graph of how the sensed magnetic flux density varies as the angle of the opened refrigerator door 1 varies. The magnet-to-sensor distances at which the switch changes state depends on the BOP and BRP. If you want to determine the typical distance at which the sensor switches state, find the locations on the Figure 1-3 plot where the sensed magnetic flux density values are equal to the BOP,TYP and BRP,TYP specifications listed in the device data sheet. Alternatively, when determining the worst-case device to device variation for output switching, refer to the BOP,Max and BRP,Min specifications. BOP,Max and BRP,Min account for process variation, temperature and voltage. Designing the system within these bounds will result with consistent operation despite these variables.

Figure 1-3 Magnetic Flux Density vs Refrigerator Angle of Opening (Refrigerator 1).

As an example, let’s say there are two Hall-effect switches with the following specs:

  • Switch 1

    • BRP,MIN =5.12 mT

    • BRP,TYP =6.87 mT

    • BOP,TYP =7.87 mT

    • BOP,MAX =9.62 mT

  • Switch 2

    • BRP,MIN =0.73 mT

    • BRP,TYP =1.58 mT

    • BOP,TYP =2.58 mT

    • BOP,MAX =3.43 mT

If switch 1 is used in refrigerator 1, the output of switch 1 will be low when the angle of opening for door 1 is ≤1.8°, regardless of variations in process variation, temperature, and voltage. The angle of opening for door 1 is ≤1.8° when the sensed magnetic flux density is greater than the 9.62 mT BOP,MAX. However, the typical distance where the output of switch 1 is asserted low would be at 2°, which is when the sensed magnetic flux density equals the device’s BOP,TYP value of 7.87 mT. The output of switch 1 will be high when angle of opening for door 1 is ≥2.5°, which is when the sensed magnetic flux density is less than the 5.12 mT BRP,MIN. The typical distance where the output of switch 1 is asserted high, however, would be at 2.2°.

If switch 2 is used in refrigerator 2, the typical distance at which the output of switch 2 is asserted low would be at 3.5°. The output would be low at an angle ≤3.1° regardless of variations in process variation, temperature, and voltage. Additionally, the output of switch 2 would be asserted high at 4.4° typically. The output would be asserted high at an angle ≥6.0° regardless of variations. The different switching distances of switches 1 and 2 shows how switching distance is dependent on the BOP and BRP specs of a Hall sensor.