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Unipolar Switches Provide High Voltage Transient Protection

Thu, 01/20/2011 - 10:50am
A1152/3/5/6 devicesAllegro MicroSystems, Inc. introduces a new line of two-wire, unipolar, Hall-effect switches to complement its existing family of devices used in seat belt buckle, seat position, and steering lock applications. These new devices are targeted to serve the automotive market, because they include improved high voltage transient protection, which is a feature that is critical for applications, which do not allow protection circuits to be located close to the sensor.

Allegro’s A1152/3/5/6 devices are the next generation of two-wire, unipolar, Hall-effect switches; factory trimmed to optimize the accuracy of the magnetic switch points. These devices employ a patented, high frequency, four-phase, chopper-stabilization technique to achieve magnetic stability over temperature and to eliminate offset inherent in single-element devices, when exposed to harsh automotive environments. Additionally, this advanced chopping technique provides significantly reduced jitter and faster power-on time.

Commonly found in a number of automotive applications, the A1152/3/5/6 devices are utilized to sense: seat track position, seat belt buckle presence, hood/trunk latching, steering lock position, and in shift selectors. Two-wire, unipolar switches require one less wire for operation versus the more traditional open-collector output switches. Additionally, the user gains diagnostics, as there is always current at one of two specified levels. Any output current outside of these two narrow ranges is a fault condition.

An important upgrade to this family is the on-chip transient protection and a Zener clamp to protect against over-voltage conditions on the supply line. This improved high voltage transient protection allows these devices to survive ISO 7637-2 and 40 V load dump for <0.5 seconds with minimal, and sometime no, protection from discrete components. The ESD protection has been enhanced, such that these are capable of handling a transient of 8.0 kV Human Body Model (HBM).

All family members are offered in two package styles: the “LH” is a SOT-23W style, miniature low profile package for surface-mount applications, and, in the coming months, the “UA” is a TO-92 style, three-lead, ultra-mini, Single Inline Package (SIP) for through-hole mounting.

Further information about Allegro can be found at www.allegromicro.com.
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