ATS617LSG datasheet(12/16 Pages) ALLEGRO

12 / 16 page

Dynamic, Self-Calibrating, Peak-Detecting, Differential

Hall Effect Gear Tooth Sensor IC

ATS617LSG

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Superior Performance The ATS617 peak-detecting differen-

tial design has several advantages over conventional Hall-effect

gear-tooth sensors. The signal-processing techniques used in the

ATS617 solve the catastrophic issues that affect the functionality

of conventional digital gear-tooth sensors, 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-calibra-

tion 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 detection 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 detector cir-

cuitry 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 ATS617 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 is superior in most applications to the classical single-ele-

ment design. The single-element configuration commonly 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.

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

Figure 5. Affect of varying air gaps on differential circuits.

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