ATS611LSB datasheet(10/16 Pages) ALLEGRO

10 / 16 page

ATS610LSA AND ATS611LSB

DYNAMIC, PEAK-DETECTING,

DIFFERENTIAL HALL-EFFECT

GEAR-TOOTH SENSORS

115 Northeast Cutoff, Box 15036

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

DEVICE DESCRIPTION — Continued

Differential vs. Single-Element Sensing. The differen-

tial Hall-element configuration is superior in most applica-

tions 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, with valley widths, with eccentrici-

ties, and with vibration. The differential configuration

cancels the effects of the back-biased field and avoids

many of the issues presented by the single Hall element.

NOTE — 10 G = 1 mT, exactly.

Peak-Detecting vs. AC-Coupled Filters. High-pass

filtering (normal ac coupling) is a commonly used tech-

nique for eliminating circuit offsets. AC coupling has

errors at power up because the filter circuit needs to hold

the circuit zero value even though the circuit may power

up over a large signal. Such filter techniques can only

perform properly after the filter has been allowed to settle,

which is typically greater than one second. Also, high-

pass filter solutions cannot easily track rapidly changing

baselines such as those caused by eccentricities. Peak

detection switches on the change in slope of the signal

and is baseline independent at power up and during

running.

Track-and-Hold Peak Detecting vs. Zero-Crossing

Reference. The usual differential zero-crossing sensors

are susceptible to false switching due to off-center and

tilted installations, which result in a shift in baseline that

changes with air gap. The track-and-hold peak-detection

technique ignores baseline shifts versus air gaps and

provides increased immunity to false switching. In addi-

tion, using track-and-hold peak-detecting techniques,

increased air gap capabilities can be expected because a

peak detector utilizes the entire peak-to-peak signal range

as compared to zero-crossing detectors that switch on

fixed thresholds.

NOTE — “Baseline” refers to the zero-gauss differen-

tial where each Hall-effect element is subject to the

same magnetic field strength.

Differential flux maps vs. air gaps

Single-element flux maps

showing the impact of varying valley widths

1500

-1500

ANGLE OF TARGET ROTATION IN DEGREES

1000

-500

-1000

Dwg. GH-061

500

= 25

°C

TARGET

AIR GAP = 2.5 mm

AIR GAP = 2.0 mm

AIR GAP = 1.5 mm

AIR GAP = 0.5 mm

AIR GAP = 1.0 mm

-2000

-5000

ANGLE OF TARGET ROTATION IN DEGREES

-2500

-4000

-4500

Dwg. GH-061-1

-3500

-3000

= 25

°C

TARGET

AIR GAP = 0.5 mm

AIR GAP = 1.0 mm

AIR GAP = 1.5 mm

AIR GAP = 2.5 mm

AIR GAP = 2.0 mm

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