Allegro MicroSystems Europe - PRODUCT NEWS
  
 
Programmable, chopper-stabilised,
Hall-effect Switches 
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 consists of a single-element chopper-stabilised Hall-effect integrated circuit that 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 in the presence of a sufficiently large south-pole magnetic field, while 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 proprietary dynamic offset cancellation technique, with an internal high-frequency clock, minimises the residual offset voltage, which is normally caused by device overmoulding, temperature dependencies, and thermal stress. This technique produces devices that have an extremely stable quiescent output voltage, are immune to mechanical stress, and have precise recoverability after temperature cycling. Many problems normally associated with low-level analogue signals are minimised by having the Hall element and amplifier in a single chip. Output precision is obtained by internal gain adjustments during the manufacturing process and operating-point programming in the user's application. Other features include on-chip supply-transient protection, output short-circuit protection, and reverse battery protection. These sensor systems are ideal for use in gathering speed, position, and timing information using gear-tooth based configurations. They are particularly suited to those applications that require accurate duty cycle control or accurate edge detection. The small package can be easily assembled and used in conjunction with a wide variety of gear/target shapes and sizes. The devices' ability to withstand high temperatures makes them ideally suited to automotive applications, while their low vibration sensitivity makes them extremely useful for transmission speed sensing. The A3250 and A3251 are available for operating temperature ranges of -40°C to +85°C and -40°C 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. __________________________________________________ Allegro MicroSystems Europe

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December 2000

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