ATS612LSG Allegro MicroSystems, Inc., ATS612LSG Datasheet - Page 7

• Manufacturer Part Number: ATS612LSG
• Description: Ats612lsg Dynamic Self-calibrating Peak-detecting Differential Hall-effect Gear-tooth Sensors
• Manufacturer: Allegro MicroSystems, Inc.

Assembly Description. The ATS612 gear-tooth sensor
is a Hall IC/magnet configuration that is fully optimized to
provide digital detection of gear tooth edges. This
sensor is packaged in a molded miniature plastic body
that has been optimized for size, ease of assembly, and
manufacturability. High operating temperature materials
are used in all aspects of construction.
The use of this sensor is simple. After proper power is
applied to the component the sensor is then capable of
instantly providing digital information that is
representative of the profile of a rotating gear. No
additional optimization or processing circuitry is required.
This ease of use should reduce design time and
incremental assembly costs for most applications.
Sensing Technology. The gear tooth sensor module
contains a single-chip differential Hall effect sensor IC, a
Samarium Cobalt magnet, and a flat ferrous pole piece
(Figure 2). The Hall IC consists of 2 Hall elements
(spaced 2.2 mm apart) located so as to measure the
magnetic gradient created by the passing of a ferrous
object. The two elements measure the magnetic
gradient and convert it to an analog voltage that is then
processed in order to provide a digital output signal.
Internal Electronics. The processing circuit uses a
patented peak detection scheme to eliminate magnet
and system offsets. This technique allows dynamic
coupling and filtering of offsets without the power-up and
settling time disadvantages of classical high-pass
filtering schemes. The peak signal of every tooth and
valley is detected by the filter and is used to provide an
instant reference for the operate and release point
DEVICE DESCRIPTION
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Magnetic Circuit
Figure 2
DIFFERENTIAL HALL-EFFECT GEAR TOOTH SENSOR
DYNAMIC, SELF-CALIBRATING, PEAK-DETECTING,
ATS612LSG
comparator. In this manner, the thresholds are adapted
and referenced to individual signal peaks and valleys,
providing immunity to zero line variation from installation
inaccuracies (tilt, rotation, and off center placement), as
well as for variations caused by target and shaft
eccentricities. The peak detection concept also allows
extremely low speed operation for small value filter
capacitors.
The ATS612 also includes self-calibration circuitry that is
engaged at power on. The signal amplitude is measured
and the device gain is normalized. In this manner,
switch-point drift versus air gap is minimized and
excellent timing accuracy can be achieved. The AGC
(Automatic Gain Control) circuitry, in conjunction with a
unique hysteresis circuit, also eliminates the effect of
gear edge overshoot as well as increases the immunity
to false switching caused by gear tooth anomalies at
close air gap. The AGC circuit sets the gain of the
device after power on. Up to 0.25 mm air gap change
can occur after calibration is complete without significant
performance impact.
Superior Performance. The ATS612 peak-detecting
differential gear-tooth sensor module has several
advantages over conventional Hall-effect gear-tooth
sensors. The signal-processing techniques used in the
ATS612 solve the catastrophic issues that affect the
functionality of conventional digital gear-tooth sensors.
Temperature drift. Changes in temperature do not
greatly affect this device due to the stable amplifier
design and the offset rejection circuitry.
Timing accuracy variation due to air gap. The
accuracy variation caused by air gap changes is
minimized by the self-calibration circuitry. A 2x-to-3x
improvement can be seen.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
Copyright © 2001, 2003 Allegro MicroSystems, Inc.