True Zero-Speed Low-Jitter High Accuracy

Gear Tooth Sensor

ATS625LSG

10

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036

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

www.allegromicro.com

Sensor Description

Figure 2. Device Cross Section. Relative motion of the target is detected

by the dual Hall elements mounted on the Hall IC. This view is from the

side opposite the pins.

Figure 3. This left-to-right (pin 1 to pin 4) direction of target rotation

results in a high output signal when a tooth of the target gear is centered

over the face of the sensor. A right-to-left (pin 4 to pin 1) rotation inverts

the output signal polarity.

Target (Gear)

Back-biasing Magnet

South Pole

North Pole

Plastic

(Pin 1 Side)

(Pin

n >1 Side)

Hall IC

Pole Piece

Element Pitch

(Concentrator)

Dual-Element

Hall Effect Device

Hall Element 1

Hall Element 2

of Sensor

Rotating Target

Branded Face

1

4

Assembly Description

The ATS625LSG true zero-speed gear tooth sensor is a com-

bined Hall IC-magnet configuration that is fully optimized to

provide digital detection of gear tooth edges. This sensor is

integrally molded into a plastic body that has been optimized for

size, ease of assembly, and manufacturability. High operating

temperature materials are used in all aspects of construction.

Sensing Technology

The gear tooth sensor contains a single-chip differential Hall

effect sensor IC, a 4-pin leadframe, a samarium cobalt magnet,

and a flat ferrous pole piece. The Hall IC consists of two Hall

elements spaced 2.2 mm apart, and each independently measures

the magnetic gradient created by the passing of a ferrous object.

This is illustrated in figures 2 and 3. The differential output of

the two elements is converted to a digital signal that is processed

to provide the digital output.

Switching Description

After proper power is applied to the component, the sensor is

then capable of providing digital information that is representa-

tive of the profile of a rotating gear, as illustrated in figure 4.

No additional optimization is needed and minimal processing

circuitry is required. This ease of use reduces design time and

incremental assembly costs for most applications.

Figure 4. The magnetic profile reflects the geometry of the target, allowing the device to present an accurate digital output response.

Target

Mechanical Profile

Target

Magnet ic Profile

Sensor Out put

Elect rical Profile

Target Motion from

Pin 1 to Pin 4

Sensor Out put

Elect rical Profile

Target Motion from

Pin 4 to Pin 1

Signature Tooth

B+

B

IN

V+

V

OUT

V+

V

OUT

Sensor Output

Switch State

On

Off

On

Off

On

Off

On

Off

On

Off

On

Off

On

Off

On

Off