A1684: Two-Wire, Zero-Speed, High Accuracy Differential Sensor IC


The A1684LUB is an optimized Hall-effect sensing integrated circuit that provides a user-friendly solution for true zero-speed digital ring magnet and—when magnetically back-biased—gear tooth sensing in two-wire applications. The Hall-effect IC has been optimized for the automotive environment. This small package can be used in conjunction with a wide variety of target shapes and sizes.

The single integrated circuit incorporates a dual element Hall effect sensor IC and signal processing circuitry that switches in response to differential magnetic signals created by a ring magnet, or by a rotating ferromagnetic target when used in combination with a back-biasing magnet. The device contains a sophisticated compensating circuit to eliminate magnetic and system offsets. Digital tracking of the analog signal is used to achieve true zero-speed operation. Advanced calibration algorithms are used to adjust the device gain and offset at power-up, resulting in air gap independent switchpoints, which greatly improves output accuracy. In addition, advanced running mode calibration circuits mitigate the effect of system anomalies such as target vibration and sudden changes in air gap.

The regulated current output is configured for two-wire operation. When configured with a back-biasing magnet, this sensor IC is ideal for obtaining edge and duty cycle information in gear-tooth–based applications such as transmission speed.

The A1684 is provided in a 2-pin miniature SIP package (suffix UB) that is lead (Pb) free, with 100% matte tin leadframe plating.

Featured Video:

Differential Speed Sensor Systems

Differential Speed Sensor System Solutions

Seth Prentice, Strategic Marketing Manager for Allegro MicroSystems Speed Sensor IC group, discusses IC solutions for designing speed sensing applications including automotive transmissions, washing machine drum speeds, and fork lift positioning requiring reliable consistent output signals. Watch Video

Top Features

  • Integrated capacitor reduces requirement for external EMI protection component
  • Fully optimized differential digital ring magnet and gear tooth sensor IC
  • Running Mode Lockout
  • Unique algorithms to assist in mitigation of system anomalies such as vibration
  • AGC and reference adjust circuit
  • Air gap independent switchpoints
  • Digital output representing target mechanical profile
  • Precise duty cycle throughout operating temperature range
  • Short power-on time
  • True zero-speed operation
  • Undervoltage lockout (UVLO)
  • Wide operating voltage range
  • Internal current regulator for two-wire operation
  • Robust test coverage capability using Scan Path and IDDQ measurement
  • AEC-Q100 automotive qualified

Part Number Specifications and Availability

Part Number Package Type Temperature RoHS
Part Composition /
RoHS Data
Comments Samples Check Stock
A1684LUBTN-T 2-lead SIP -40°C to 150°C Yes View Data Contact your
local sales rep
Distributor Stock

Allegro’s products are not to be used in any devices or systems, including but not limited to life support devices or systems, in which a failure of Allegro’s product can reasonably be expected to cause bodily harm.

Allegro 2-Pin SIP UB Package


The A1684 is available in a lead (Pb) free 2-pin SIP (Suffix UB) package with a 100% matte tin plated leadframe.

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