Wednesday, January 19, 2011

Two-wire Hall-effect unipolar switches

The new A1152/3/5/6 from Allegro MicroSystems Europe are a range of two-wire unipolar Hall-effect switches designed for automotive sensing applications in seat-belt buckle, seat position, and steering lock applications.

The new devices are produced using the Allegro® advanced BiCMOS wafer fabrication process, and include improved high-voltage transient protection: a critical factor for automotive applications where external protection circuitry cannot be located close to the sensor.

These Hall-effect switches are factory trimmed to optimise the accuracy of the magnetic switch points, and employ a patented high-frequency four-phase chopper-stabilisation technique to achieve magnetic stability over temperature and to eliminate the offset inherent in single-element devices, when exposed to harsh automotive environments. The advanced chopping technique also provides significantly reduced jitter and shorter power-on times.

Two-wire unipolar switches require one less wire for operation than the more traditional open-collector output switches, and also offer diagnostic capability as there is always current present at one of two specified levels. Any output current outside these two narrow ranges is a fault condition.

In addition to the on-chip transient protection, a Zener clamp protects against overvoltage conditions on the supply line. The enhanced high-voltage transient protection allows these devices to survive ISO 7637-2 and 40 V load dump for up to 0.5 seconds with minimal, and sometimes no, protection from discrete components. Electrostatic discharge protection has also been enhanced to the extent that the devices are capable of handling a transient of 8.0 kV Human Body Model (HBM).

The A1152/3/5/6 devices are utilised in automotive applications to sense seat track position, seat-belt buckle presence, bonnet and boot latching, and steering-lock position, as well as in gear-shift selectors.

All family members will be offered in two package styles: the SOT-23W miniature low-profile package for surface-mount applications (suffix LH) and the TO-92 style three-lead "ultra-mini" single inline package (SIP) for through-hole mounting (suffix UA).

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