ATS685LSH: Two-Wire, Zero Speed Differential Gear Tooth Sensor IC


The ATS685LSH is an optimized Hall-effect sensing integrated circuit and rare-earth pellet combination that provides a user-friendly solution for true zero-speed digital gear-tooth sensing in two-wire applications. The sensor IC consists of a single-shot molded plastic package that includes a samarium cobalt pellet, a pole piece, and a Hall Effect IC that has been optimized to the magnetic circuit. This small package can be assembled simply and used in conjunction with a wide variety of gear 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 ferromagnetic targets. 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 algorithms 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. This sensor IC is ideal for obtaining edge and duty cycle information in gear-tooth–based applications such as transmission speed.

The ATS685 is provided in a 4-pin SIP package that is lead (Pb) free, with 100% matte tin leadframe plating.

Top Features

  • Fully optimized differential digital gear tooth sensor IC
  • Running Mode Lockout
  • Unique algorithms for increased vibration immunity
  • AGC and reference adjust circuit
  • Air gap independent switchpoints
  • Digital output representing gear profile
  • Precise duty cycle throughout operating temperature range
  • Large operating air gap range
  • Short power-on time
  • True zero-speed operation
  • Undervoltage lockout (UVLO)
  • Wide operating voltage range
  • Internal current regulator for two-wire operation
  • Single-chip sensing IC for high reliability
  • Robust test coverage capability using Scan Path and IDDQ measurement

Part Number Specifications and Availability

Part Number Package Type Temperature RoHS
Part Composition /
RoHS Data
Comments Samples Check Stock
ATS685LSHTN-T 4-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.


The ATS685 is provided in a 4-pin SIP (suffix SH) package that is lead (Pb) free, with 100% matte tin leadframe plating.

SH SIP 4 pin

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