9

ATS643-DS, Rev. 1

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

115 Northeast Cutoff, Box 15036

www.allegromicro.com

Allegro MicroSystems, Inc.

Self-Calibrating, Zero-Speed Differential GTS with Continuous Update

ATS643LSH

Sensing Technology. The ATS643 module contains a

single-chip differential Hall effect sensor IC, a samarium cobalt

magnet, and a flat ferrous pole piece (concentrator). As shown

in figure 1, the Hall IC supports two Hall elements, which sense

the magnetic profile of the ferrous gear target simultaneously,

but at different points (spaced at a 2.2 mm pitch), generating a

precise switching of the digital output signal.

The Hall IC is self-calibrating and also possesses a tempera-

ture compensated amplifier and offset cancellation circuitry. Its

voltage regulator provides supply noise rejection throughout the

operating voltage range. Changes in temperature do not greatly

affect this device due to the stable amplifier design and the offset

rejection circuitry. The Hall transducers and signal processing

electronics are integrated on the same silicon substrate, using a

proprietary BiCMOS process.

Target Profiling During Operation. When proper power is

applied to the sensor, it is capable of providing digital informa-

tion that is representative of the mechanical features of a rotating

gear. The waveform diagram in figure 3 presents the automatic

translation of the mechanical profile, through the magnetic

profile that it induces, to the digital output signal of the ATS643.

No additional optimization is needed and minimal processing

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

Functional Description

Target (Gear)

Back-biasing Magnet

South Pole

North Pole

Case

(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

incremental assembly costs for most applications.

Determining Output Signal Polarity. In figure 3, the top

panel, labeled Mechanical Position, represents the mechani-

cal features of the target gear and orientation to the device. The

bottom panel, labeled Sensor Output Signal, displays the square

waveform corresponding to the digital output signal that results

from a rotating gear configured as shown in figure 2. That direc-

tion of rotation (of the gear side adjacent to the face of the sensor)

is: perpendicular to the leads, across the face of the device, from

the pin 1 side to the pin 4 side. This results in the sensor output

edge of a tooth (a rising mechanical edge, as detected by the

sensor) passes the sensor face. In this configuration, the device

output current switches to its high polarity when a tooth is the

target feature nearest to the sensor. If the direction of rotation is

reversed, so that the gear rotates from the pin 4 side to the pin 1

side, then the output polarity inverts. That is, the output signal

goes high when a falling edge is detected, and a valley is the

ing Characteristics table).

Continuous Update of Switchpoints. Switchpoints are the

at which the device changes output signal polarity. The value of

Figure 1. Relative motion of the target is detected by the dual Hall ele-

ments mounted on the Hall IC.

Figure 2. 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 nearest

the face of the sensor (see figure 3). A right-to-left (pin 4 to pin 1) rota-

tion inverts the output signal polarity.

Figure 3. The magnetic profile reflects the geometry of the target, allow-

ing the ATS643 to present an accurate digital output response.

On

Off

Off

On

Sensor Internal Switch State

Sensor Orientation to Target

Mechanical Position (Target movement pin 1 to pin 4)

Target

(Gear)

Sensor

Sensor Branded Face

Pin 1

Side

Pin 4

Side

+t

Target Magnetic Profile

+B

+t

+t

This tooth

sensed

earlier

This tooth

sensed

later