Description
The A1642 is an optimized Hall effect sensing integrated 
circuit that provides a user-friendly solution for true zero-speed 
digital ring-magnet sensing in two-wire applications. This small 
package can be easily assembled and used in conjunction with 
a wide variety of target shapes and sizes.
The integrated circuit incorporates dual Hall effect elements 
and signal processing that switches in response to differential 
magnetic signals created by ring magnet poles. The circuitry 
contains a sophisticated digital circuit to reduce system offsets, 
to calibrate the gain for air-gapindependent switchpoints, 
and to achieve true zero-speed operation. Signal optimization 
occurs at power-on through the combination of offset and 
gain adjust and is maintained throughout the operating time 
with the use of a running-mode calibration. The running-mode 
calibration allows immunity to environmental effects such as 
micro-oscillations of the target or sudden air gap changes.
The regulated current output is configured for two-wire 
applications and the A1642 is ideally suited for obtaining 
speed and duty cycle information in ABS (antilock braking 
systems). The 1.5 mm spacing between the dual Hall elements 
is optimized for fine pitch ring-magnetbased configurations. 
For applications requiring sensing of rotating ferrous gears and 
targets, refer to the Allegro ATS series of products. The package 
is lead (Pb) free, with 100% matte tin leadframe plating.
A1642LKN-DS, Rev. 4
Features and Benefits
?Running mode calibration for continuous optimization
?Single chip IC for high reliability
?Internal current regulator for 2-wire operation
?Precise duty cycle signal over operating temperature range
?Large operating air gaps
?Automatic Gain Control (AGC) for air gap independent 
switchpoints
?Automatic Offset Adjustment (AOA) for signal processing 
optimization
?True zero-speed operation
?Undervoltage lockout
?Wide operating voltage range
?Wide-lead package suitable for welding external 
components directly to the package leads or for welding 
the device to a leadframe.
Two-Wire True Zero-Speed Miniature Differential 
Peak-Detecting Sensor IC with Continuous Calibration
Package: 4-pin SIP (Suffix KN)
Functional Block Diagram
Not to scale
A1642
VCC
Automatic Offset
Control
AOA DAC
Hall
Amplifier
AGC DAC
Gain
Tracking
DAC
Peak Hold
Gain Control
Internal Regulator
Test Signals
GND
Test