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ATS616LSG-DS, Rev. 1

Worcester, Massachusetts 01615-0036 (508) 853-5000

115 Northeast Cutoff, Box 15036

www.allegromicro.com

Allegro MicroSystems, Inc.

Dynamic Self-Calibrating Peak-Detecting Differential Hall Effect Gear Tooth Sensor

ATS616LSG

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 peak-detecting differential

gear-tooth sensor module has several advantages over conven-

tional Hall-effect gear-tooth sensors. 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 sensors

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 sensor configura-

tion eliminates the baseline variations caused by gear run out.

Differential vs. Single-Element Sensing.

The differential

Hall-effect configuration is superior in most applications to the

classical single-element gear-tooth sensor. The single-element

configuration commonly used (Hall-effect sensor 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.

Figure 4. Affect of varying valley widths on single-element sensors.

Figure 4. Affect of varying air gaps on differential sensors.