When designing a linear magnetic sensing system, always consider these three variables: the magnet, sensing distance, and the range of the sensor. Notice from Figure 9-5, the magnetic flux density versus distance has both positive and negative values as the magnet slides on top of the sensor. There is a region approximately the same length of the magnet which produces a linear change in field. To measure the magnetic flux density across the entire range, select the TMAG5253B version with the highest sensitivity that has a B_L (linear magnetic sensing range) that is larger than the maximum magnetic flux density in the application. With this input, the user can monitor the change in position by measuring in the linear input region. Figure 9-9 shows the magnetic flux density across the three axes in the sensor location. The sensor is sensitive only to the magnetic field on Z axis, and Figure 9-7 shows the output voltage from the sensor, as the magnet slides on top of the sensor.

Notice that the linear region of sensing is only around ±3.0 mm, where the sensor output varies linearly with the position of the magnet. This linear range of operation will increase linearly with the size of the magnet. Based on the output voltage, it is determined that the sensor version with magnetic range of ±80 mT is able to cover the entire magnetic field range that is seen by the sensor. TI recommends using magnetic field simulation software and referring to magnet specifications and the mechanical placements to determine if the sensor with the right sensitivity.