Two-wire wheel-speed sensor IC with integrated capacitor

July 09, 2014 // By Graham Prophet
A1688 from Allegro MicroSystems Europe is a Hall-effect sensor IC that provides a solution for true zero-speed digital ring magnet and gear tooth sensing in two-wire automotive applications such as ABS braking systems.

The device offers performance in areas such as pitch deviation accuracy, consistent supply current distribution (better than six-sigma), low jitter and enhanced EMC performance provided by an integrated capacitor which also reduces the requirement for external components.

The integrated circuit incorporates a dual-element Hall-effect sensor and signal processing circuitry that switches in response to differential magnetic signals created by magnetic encoders, or, when properly back-biased with a magnet, from ferromagnetic targets. A digital circuit reduces magnet and system offsets, calibrates the gain for air-gap independent switch points, and provides true zero-speed operation.

Signal optimisation occurs at power-up through the combination of offset and gain adjustment, and is maintained throughout operation with the use of a running-mode calibration scheme which provides immunity from environmental effects such as micro-oscillations of the sensed target or sudden air-gap changes.

The regulated current output is configured for two-wire interface circuitry, and is suited to obtaining speed information in wheel speed applications. The Hall element spacing is optimised for high-resolution small-diameter targets.

The A1688 comes in the UB package, which integrates the IC and the high-temperature ceramic capacitor in a single overmoulded SIP package with an outside diameter of less than 6.5 mm and has wider lead spacing.

Allegro MicroSystems; www.allegromicro.com