ATS616 Datasheet, PDF (10/14 Pages) Allegro MicroSystems – Dynamic Self-Calibrating Peak-Detecting Differential Hall Effect Gear Tooth Sensor

ATS616LSG
Dynamic Self-Calibrating Peak-Detecting Differential
Hall Effect Gear Tooth Sensor IC
AGC circuit sets the gain of the device after power-on. Up to a
0.25 mm air gap change can occur after calibration is complete
without significant performance impact.
Superior Performance. The ATS616 has several advantages
over conventional Hall-effect devices. The signal-processing
techniques used in the ATS616 solve the catastrophic issues that
affect the functionality of conventional digital gear-tooth sen-
sors, such as the following:
• 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 varia-
tion caused by air gap changes is minimized by the self-cali-
bration circuitry. A 2×-to-3× improvement can be seen.
• Dual edge detection. Because this device switches based on
the positive and negative peaks of the signal, dual edge detec-
tion is guaranteed.
• Tilted or off-center installation. Traditional differential sensor
ICs can switch incorrectly due to baseline changes versus air
gap caused by tilted or off-center installation. The peak detec-
tor circuitry references the switchpoint from the peak and is
immune to this failure mode. There may be a timing accuracy
shift caused by this condition.
• Large operating air gaps. Large operating air gaps are achiev-
able with this device due to the sensitive switchpoints after
power-on (dependent on target dimensions, material, and
speed).
• Immunity to magnetic overshoot. The patented adjustable
hysteresis circuit makes the ATS616 immune to switching on
magnetic overshoot within the specified air gap range.
• Response to surface defects in the target. The gain-adjust
circuitry reduces the effect of minor gear anomalies that would
normally cause false switching.
• Immunity to vibration and backlash. The gain-adjust circuitry
keeps the hysteresis of the device roughly proportional to the
peak-to-peak signal. This allows the device to have good im-
munity to vibration even when operating at close air gaps.
• Immunity to gear run out. The differential chip configuration
eliminates the baseline variations caused by gear run out.
Differential vs. Single-Element Design. The differential chip
configuration is superior in most applications to the classical
single-element design. The single-element configuration com-
monly used (Hall-effect element mounted on the face of a simple
permanent magnet) requires the detection of a small signal (often
<100 G) that is superimposed on a large back-biased field, often
1500 G to 3500 G. For most gear/target configurations, the back-
biased field values change due to concentration effects, resulting
in a varying baseline with air gap, valley widths, eccentricities,
and vibration (figure 4). The differential configuration (figure 5)
cancels the effects of the back-biased field and avoids many of
the issues presented by the single Hall element design.
Peak Detecting vs. AC-Coupled Filters. High-pass filtering
Figure 4. Affect of varying valley widths on single-element circuits.
Figure 4. Affect of varying air gaps on differential circuits.
Allegro MicroSystems, LLC
10
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com