9

30Dec03, Rev. 1.42

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

115 Northeast Cutoff, Box 15036

www.allegromicro.com

Allegro MicroSystems, Inc.

Self-Calibrating Gear Tooth Sensor with 9-Bit Signal Capture

ATS672LSB

Typical Circuit Design

The following circuit is the most basic configuration required for

proper device operation. A pull-up resistor is used.

2

ATS672

1

3

4

VCC

0.1 uF

VOUT

Sensor/Target Evaluation

In order to establish the proper operating specification for a

particular sensor/target configuration, a systematic evaluation of

the magnetic circuit should be performed. The first step is the

generation of a magnetic map of the target. By using a cali-

brated device, a magnetic signature of the system is made. A

magnetic map of the 8X reference target, created using the LSB

sensor package, is shown below.

From this map data, a pair of curves can be derived that describe

the tooth and valley magnetic fields versus air gap. Knowing

the minimum amount of magnetic flux density that guarantees

operation of the sensor, one can determine the maximum opera-

tional air gap of the sensor/target system.

Magnetic Map, 8X Reference Target, Using LSB Package

-200

-150

-100

-50

0

50

100

150

200

250

300

350

400

450

500

0

30

60

90

120

150

180

210

240

270

300

330

360

Position (°)

-200

-100

0

100

200

300

400

500

600

00.5

11.522.5

33.5

4

4.5

5

Air Gap (mm)

8X Reference Target Using LSB Package

Magnetic Flux Density, B, Versus Air Gap

Tooth

Valley