A magnet produces a magnetic field that travels from the North pole to the South pole. The total amount of field through a 2-dimensional slice is the flux, measured in units of weber. Webers per square meter indicates flux density, measured in units of tesla (T). The unit of gauss (G) also describes flux density, where 1 T = 10000 G. In millitesla, 1 mT = 10 G. Tesla is the official SI unit and used by TI data sheets, but other sources may use gauss.

• The flux density increases closer to a magnet.
• The flux density at the surface of the magnet depends on its material and the amount of magnetization.
• At a given distance, physically large magnets project a larger flux density.

The symbol B is used for flux density. Most TI Hall sensors use the convention that magnetic fields traveling from the bottom of the device through the top are positive B, and fields traveling from the top to the bottom of the device are negative B. One exception is the TMAG5273 linear 3D Hall-effect sensor, which defines a positive field as when the magnetic fields travel from the top of the device to the bottom. Out-of-plane one dimensional (1D) position sensors are sensitive to the magnetic field component that is perpendicular to the die inside the package. On the other hand, in-plane 1D position sensors are sensitive to application of the magnet pole in the same plane as the die. 3D linear Hall sensors use one out-of-plane sensing element and two in-plane sensing elements to detect across three directions.

Figure 3-1 Typical Polarity of Field Directions For 1D Out-of-Plane Sensors