Self-Calibrating TPOS Gear Tooth Sensor Optimized

for Automotive Cam Sensing Applications

ATS673 and

ATS674

9

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036

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

www.allegromicro.com

Operational Description

Figure 2. Device Cross Section. Motion of the target is detected by the Hall element mounted on the Hall IC. Panel A, the presence of a tooth feature on

the target is distinguished by a high magnetic flux density, B. Panel B, the presence of a valley feature is distinguished by its low magnetic flux density.

Assembly Description

The ATS673 and ATS674 true zero-speed gear tooth sensors

have a 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 Hall effect sen-

sor IC, a 4-pin leadframe and a specially designed rare-earth

magnet. The Hall IC supports a Hall element that measures the

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

is illustrated in figure 2. The difference in the magnetic gradients

created by teeth and valleys allows the devices to generate a

digital output signal.

Output

After proper power is applied to the devices, they are then

capable of providing digital information that is representative of

the profile of a rotating gear, as illustrated in figure 3. No addi-

tional optimization is needed and minimal processing circuitry is

required. This ease of use reduces design time and incremental

assembly costs for most applications.

Figure 3. The magnetic profile reflects the geometry of the target, allowing the device to present an accurate digital output response.

Target (Gear)

Sensor Device

High-B field

Back-Biasing magnet

Plastic

Hall element

Leadframe

Hall IC

Low-B field

Pole piece

(Concentrator)

North Pole

South Pole

(A)

(B)

Target

Mechanical Profile

Target

Magnet ic Profile

Sensor Out put

Elect rical Profile

Sensor Out put

Elect rical Profile

-HT Option

-LT Option

B

0

B

IN

V+

V

OUT

V+

V

OUT

Sensor Output

Switch State

On

Off

On

Off

On

Off

On

Off

Sensor Output

Switch State

On

Off

On

Off

On

Off

On

Off