Switches, Relays & Keypads


Programmable chopper-stabilised Hall-effect switches

28 February 2001 Switches, Relays & Keypads

The A3250 and A3251 from Allegro MicroSystems are a new range of programmable Hall-effect sensor/switches that are ideally suited to proximity or gear-tooth sensing in automotive and industrial applications.

Each sensor can be programmed to the desired magnetic switch point, allowing optimisation of the sensor airgap and timing accuracy performance after final packaging. The A3250's output turns on, and the A3251 turns off, with a sufficiently large south-pole magnetic field.

Each sensor incorporates a single-element Hall IC that switches in response to magnetic signals created by a ferrous target. The programmability of the circuit eliminates magnet and system offsets such as those caused by tilt, yet provides zero-speed detection capabilities without the associated running jitter inherent in classical digital solutions.

A propriety dynamic offset cancellation technique, with an internal high-frequency clock, minimises the residual offset voltage. Many problems normally associated with low-level analog signals are minimised by having the Hall element and amplifier in a single chip.

Other features include on-chip supply-transient protection, output short-circuit protection, and reverse battery protection.

The A3250 and A3251 are available for operating temperature ranges of -40 to +85°C and -40 to +150°C. Two package styles - a miniature SOT-89/TO-243AA transistor package for surface-mount applications and a three-lead ultra-miniature single-inline package for through-hole mounting - provide a magnetically optimised configuration for most applications.



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