Hall-effect latch suits speed & position sensing

11th September 2015
Barney Scott

The A1245 from Allegro MicroSystems Europe is a two-wire Hall-effect latch with high magnetic sensitivity and excellent EMC performance in automotive and industrial speed/position sensing applications. The A1245 latch is produced using Allegro's advanced BiCMOS wafer fabrication process, and implements a high-frequency 4-phase chopper-stabilisation technique to achieve magnetic stability from -40 to +150°C.

Two-wire latches of this type are particularly advantageous in cost-sensitive applications because they require one less wire for operation compared with the more traditional open-collector output switches. In addition, the system designer inherently gains diagnostic capabilities 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.

The A1245 Hall-effect latch is in the high output current state in the presence of a magnetic south polarity field of sufficient magnitude, and remains in this state until a sufficient north polarity field is present.

The A1245 is designed for speed and position sensing of ring magnets or other moving/rotating assemblies in applications that are safety-critical and/or have long wiring harnesses. Typical automotive applications include internal mode switch transmissions and transmission range switch/manual lever position sensor shift selectors; electronic parking brake motors; electronic power steering; and sunroof, tailgate and other motors. The device is also suited to industrial and consumer applications including white goods, industrial control and factory automation, and automatic doors.

Overall ruggedness, including industry leading ISO 7637-2 performance, is achieved using an integrated voltage regulator, clamping diodes, ESD protection, and reverse-battery protection. The A1245 is offered in two package styles. The LH is a SOT-23W style miniature low-profile package for surface-mount applications, while the UA is a 3-pin ultra-miniature single inline package for through-hole mounting. Both packages are RoHS-compliant with 100% matt tin lead-frame plating. The device is also offered with a choice of current levels corresponding to its off or low state.

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