The A1147 and A1148 devices are two-wire, unipolar, Hall effect switches that are factory-programmed at end-of-line to optimize ultrasensitive magnetic switchpoint accuracy. These devices use a patented high frequency chopper-stabilization technique, produced using the Allegro advanced BiCMOS wafer fabrication process, to achieve magnetic stability and to eliminate offset inherent in single-element devices exposed to harsh application environments.
Commonly found in a number of automotive applications, these switches are utilized to sense seat track position, seat belt buckle presence, hood/trunk latching, and shift selector position. Two-wire unipolar switches, such as the A1147 and A1148, are particularly advantageous in price-sensitive applications because they require one less wire for operation than do switches with the more traditional open-collector output. Additionally, the system designer inherently gains diagnostics because there is always output current flowing, which should be in either of two narrow ranges. Any current level not within these ranges indicates a fault condition. These devices also feature on-chip transient protection and a Zener clamp to protect against overvoltage conditions on the supply line.
The output currents of the A1148 switches HIGH in the presence of a south (+) polarity magnetic field of sufficient strength, and switches LOW otherwise, as in the presence of a weak field or a north (–) polarity field. The A1147 has an opposite output: the currents switch LOW in the presence of a south-polarity magnetic field of sufficient strength, and switch HIGH otherwise.
Both versions are offered in two package styles. The LH is a SOT-23W, miniature low-profile package for surface-
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