Description

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

thandoswitcheswiththemoretraditionalopen-collectoroutput.

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

A1147-DS, Rev. 8

Features and Benefits

▪ Chopper stabilization

▫ Low switchpoint drift over operating

temperature range

▫ Low sensitivity to stress

▪ Factory programmed at end-of-line for optimized

switchpoints

▪ On-chip protection

▫ Supply transient protection

▫ Reverse-battery protection

▫ On-board voltage regulator

▫ 3.5 to 24 V operation

Low Current Ultrasensitive Two-Wire Chopper-Stabilized

Unipolar Hall Effect Switches

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Functional Block Diagram

Not to scale

Packages: 3 pin SOT23W (suffix LH), and

3 pin SIP (suffix UA)

A1147 and A1148

Amp

Regulator

Low-Pass

Filter

GND

VCC

GND

Package UA Only

0.01 uF

V+

Clock/Logic

To All Subcircuits