A1128: Highly Programmable Hall-Effect Switch


The A1128 is a field-programmable, unipolar Hall-effect switch designed for use in high-temperature applications. This device uses a chopper-stabilization technique to eliminate offset inherent in single-element devices.

The devices are externally programmable. A wide range of programmability is available on the magnetic operate point, BOP , while the hysteresis remains fixed. This advanced feature allows optimization of the sensor IC switchpoint and can drastically reduce the effects of mechanical placement tolerances found in end-use production environments.

A proprietary dynamic offset cancellation technique, with an internal high-frequency clock, reduces the residual offset voltage, which is normally caused by device overmolding, temperature dependencies, and thermal stress. Having the Hall element and amplifier in a single chip minimizes many problems normally associated with low-level analog signals.

Two package styles provide a magnetically optimized package for most applications. Type LT is a miniature SOT89/TO-243AA surface mount package that is thermally enhanced with an exposed ground tab, and type UA is a three-lead ultramini SIP for through-hole mounting. The packages are lead (Pb) free, with 100% matte tin plated leadframes.

The A1128LLTTR-T package variant status is Last-Time Buy. This indicates this package variant has reached the end of its life cycle and will no longer be offered by Allegro. This package variant is considered obsolete and customer notification has been provided. All orders are accepted as final builds. Samples are no longer available. Recommended replacement: A1128LUATS-T.

Top Features

  • Chopper stabilization for stable switchpoints throughout operating temperature range
  • Externally programmable:
    • Operate point (through the VCC pin)
    • Output polarity
    • Output fall time for reduced EMI in automotive applications
  • On-board voltage regulator for 3 to 24 V operation
  • On-chip protection against:
    • Supply transients
    • Output short-circuits
    • Reverse battery condition

Part Number Specifications and Availability

Part Number Package Type Temperature RoHS
Part Composition /
RoHS Data
Comments Samples Check Stock
A1128LLTTR-T 3-lead SOT -40°C to 150°C Yes View Data Last time buy Contact your
local sales rep
Distributor Stock
A1128LUA-T 3-lead SIP -40°C to 150°C Yes View Data Contact your
local sales rep
Distributor Stock
A1128LUATS-T 3-lead SIP -40°C to 150°C Yes View Data Contact your
local sales rep
Distributor Stock

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