User-programmable Hall-effect switches

The A1190/2/3 family, new from Allegro MicroSystems Europe, are a range of user-programmable Hall-effect switches that complement the company’s existing family of devices used in automotive seat-belt buckle, seat position, and gear-shift selector applications. These new devices incorporate enhanced high-voltage transient protection: a critical feature for automotive applications that do not allow protection circuits to be located close to the sensor.

The two-wire unipolar Hall-effect switches can be trimmed by the user to optimise magnetic switch point accuracy in the application. These devices are produced by the Allegro advanced BiCMOS wafer fabrication process, which implements a patented high-frequency four-phase chopper-stabilisation technique. This is claimed to achieve magnetic stability over the full operating temperature range and eliminate offsets inherent in devices with a single Hall element that are exposed to harsh application environments.

Two-wire unipolar switches are suitable for cost-sensitive automotive applications because they require one less wire for operation than the more traditional open-collector output switches. In addition, the 0system designer inherently gains diagnostic capabilities, because there is always output current flowing in one of two narrow ranges. Any current level not within these ranges indicates a fault condition. On-chip transient protection, along with a Zener diode clamp, minimises the effects of overvoltage conditions on the supply line.

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