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Sensors/MEMS??

Linear sensor eyes position-sensing apps

Posted: 17 Apr 2009 ?? ?Print Version ?Bookmark and Share

Keywords:linear sensor? position sensing automotive? Hall-effect sensor?

A1354 Hall-effect linear sensor

The new A1354 from Allegro MicroSystems Europe is a high-precision, programmable two-wire Hall-effect linear sensor that provides a pulse width modulated (PWM) output with a duty cycle proportional to an applied magnetic field. The new device is the first linear Hall-effect sensor from Allegro to include a voltage regulator, which allows the device to be powered directly from a battery with a forward supply voltage in the range from 4.5V to 18V.

The A1354 converts an analog signal from its internal Hall sensor element to a digitally encoded PWM output signal. The coupled noise immunity of the digitally encoded PWM output is superior to the noise immunity of an analog output signal.

This new device is targeted at position-sensing applications in the automotive and industrial sectors, particularly where diagnostic capabilities are required, where there is a limitation on the number of wires to and from a control unit, or where noise immunity over long wires is required.

The A1354 incorporates a monolithic BiCMOS circuit integrating a Hall element, precision temperature-compensating circuitry to reduce the intrinsic sensitivity and offset drift of the Hall element, a small-signal high-gain amplifier, proprietary dynamic offset cancellation circuits, and PWM conversion circuitry.

The dynamic offset cancellation circuitry reduces the residual offset voltage of the Hall element, which is normally caused by device overmoulding, temperature dependencies and thermal stress. The high-frequency offset cancellation (chopping) clock allows for a greater sampling rate, which increases the accuracy of the output signal and results in faster signal processing capability.

Programmable features include sensitivity, PWM frequency (15Hz or 120Hz) and unidirectional or bidirectional sensing. Programmability allows the device to be fine-tuned in the final application for higher system accuracy.

A typical application is liquid-level sensing in automotive fuel tanks, where the number of wires going into the fuel tank is limited and the length of the wires to the control units may be long enough to introduce noise coupling.

Output duty cycle clamps provide short circuit diagnostic capabilities, while a test mode at start-up allows users to calibrate out the effects of ground potential and threshold variance at start-up in automotive engine control unit applications.

The A1354 sensor is supplied in a low-profile (1mm thick) Pb-free 4-pin single inline package (KT suffix), with 100 percent matt tin lead frame plating. Operating temperature range is -40C to +125C.

- Henri Arnold
EE Times Europe





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