Innovative construction puts new twist on old principle
By Bill Schweber -- EDN, September 27, 2005
Designers have used millions of Hall-effect sensors for contactless switching and position sensing, but rotary sensing using this phenomenon has mechanical and alignment difficulties. A new design from Melexis overcomes the limitations and provides noncontact 360° rotary sensing using an inexpensive magnet with self-compensation for inherent, unavoidable drift. Vincent Hiligsmann, product-marketing manager for automotive sensors, says “The manufacturing and thermal tolerances are compensated at the IC level.”
The MLX90316 uses four Hall sensors and support circuitry and builds a ferromagnetic concentrator disk above the Hall devices to steer the flux lines in the z-axis direction. The result is that device senses in the x, y, and z planes. The outputs of the Hall sensors go to signal-conditioning circuitry, A/D converters, a DSP/microcontroller, and D/A converters, to yield output information in multiple formats. The formats include analog-sine/cosine, quadrature x/y signals, which imply rotary angle, along with a 12-bit PWM output and a digital-serial-protocol output. By design, the user-programmable monolithic device is ratiometric and thus is relatively insensitive to inevitable variations in flux-density strength due to temperature, aging, and air-gap variations.
The surface-mount device is available in an eight-lead SOIC for conventional applications or as a redundant design with two fully independent, isolated die in a TSSOP-16 package for critical applications, such as automotive steering or throttle (accelerator) sensing. The design also includes self-checking and internal diagnostics. The MLX90316 Triaxis Hall device sells for less than €1 ($1.20) in high volume.
Melexis Microelectronic Integrated Systems NV, www.melexis.com.
