Trend No. 3: The miniaturization of overall end-product form factors

The third trend relates to the miniaturization of magnetic system designs. The reasons to reduce the size of a product are many – cost, better user experience, sleeker look and feel – and doing so often involves reducing the magnet size or using multiaxis sensors. Another approach with little risk is to reduce board size by migrating to the smallest and most integrated components that the manufacturing flow will allow. To address these concerns, Texas Instruments offers small-size solutions in extra-small outline no-lead (X2SON) (1.1mm² by 1.4mm²) and wafer chip-scale packaging (WCSP) (0.8mm² by 0.8mm²). One example of high integration in a small package is the TMAG3001, which is a 3D linear solution available in WCSP.

Reducing magnet size poses a problem because it means a weaker magnetic field, therefore requiring magnetic sensors with high sensitivity. High-sensitivity solutions such as the TMAG5231 make it possible to use smaller magnets. Alternatively, you could place the magnet closer to the sensor to get an accurate measurement without a high-sensitivity solution. For weaker magnetic fields, devices with a high signal-to-noise ratio (SNR) can help ensure the most accurate measurement possible. The DRV5055 and TMAG5253 may provide as much as 70dB of SNR.

The general trend in the size reduction of end equipment is challenging for any position sensor, regardless of technology. Inductive sensors use metal targets to detect the position or presence of an object and, by meeting the guidelines as specified in data sheets, make it possible to achieve form factors as small as the side button on a fitness wristband. The main system-level requirements for inductive sensors are to have the sense coil the same size as the target, and to be within 10% to 20% of the diameter of the coil. Examples of applications trending toward smaller sizes include medical insulin pumps, surgery endoscopic tools and pneumatic cylinders in factory automation.

It is also possible to achieve miniaturization by reducing the number of components. For example, the implementation of tamper detection in an e-meter (or smart e-locks and door and window sensors) involves the use of a single 3D linear sensor instead of three Hall-effect switches or linear devices to detect tampering from large external magnets that render the e-meter incapable of accurately measuring electricity usage. Designers are using 3D magnetic sensors to improve their e-meter designs with lower power operation and adjustable external magnetic field detection devices such as the TMAG5273. With such devices there are other benefits of miniaturization with fewer components, including a single digital interface instead of multiple outputs, lower printed circuit board assembly costs and higher configurability in magnetic sensitivity.

When miniaturizing a system with fewer components, one challenge that incremental and absolute encoder designers have is how to improve the resolution of their products, which includes choosing between digital or analog output solutions. An incremental encoder monitors the speed or rate at which the magnet is moving, and also the direction. An absolute encoder can do this and know its exact position at all times with high resolution.

When incremental encoder designers use digital output Hall-effect latches, the resolution strictly depends on the number of magnetic poles in the system. Achieving higher resolution requires higher-pole-count ring magnets, and as pole dimensions get smaller, the magnetic fields produced by the magnet are inherently weaker, forcing designers to place the sensor even closer to the magnet or to use a sensor with higher sensitivity. At this point, most designers switch over to a single-chip solution with dual integrated latches such as the TMAG5111. It is important to make sure that the dual-latch solution has built-in 2D latches, which allows for the greatest flexibility in monitoring any two axes in a 3D space. Higher-resolution designs require absolute encoders with linear sensors. A single 3D linear sensor with angle measurement capability is the final migration step for high-resolution absolute encoders. Note that this implementation measures only two axes, but most 3D linear sensors have the flexibility to configure any two axes. An added bonus to using a 3D sensor is having the capability to detect a push function. Figure 4 shows trends in encoder designs.