Three-Wire True Zero-Speed Differential Peak-Detecting

Sensor IC with Continuous Calibration

ATS468

8

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

FUNCTIONAL DESCRIPTION

Sensing Technology

The ATS468 contains a single-chip differential Hall-effect sensor

IC, a permanent magnet pellet, and a flat ferrous pole piece (con-

centrator). 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

that is processed for precise switching of the digital output signal.

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

compensated amplifier and offset cancellation circuitry. The

built-in voltage regulator provides supply noise rejection through-

out the operating voltage range. Changes in temperature do not

greatly affect this device due to the stable amplifier design and

the offset compensation circuitry. The Hall transducers and signal

processing electronics are integrated on the same silicon sub-

strate, using a proprietary BiCMOS process.

Target Profiling During Operation

An operating device is capable of providing digital information

that is representative of the mechanical features of a rotating gear.

The waveform diagram in Figure 3 presents the automatic trans-

lation of the mechanical profile, through the magnetic profile that

it induces, to the digital output signal of the ATS468. 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.

Determining Output Signal Polarity

In Figure 3 the top panel, labeled Mechanical Position, represents

the mechanical features of the target gear and orientation to the

device. The bottom panel, labeled Device Output Signal, displays

the square waveform corresponding to the digital output signal

that results from a rotating gear configured as shown in Figure 2,

and electrically connected as in Figure 6. That direction of rota-

tion (of the gear side adjacent to the package face) is: perpen-

dicular to the leads, across the face of the device, from the pin 1

side to the pin 4 side. This results in the IC output switching from

low state to high state as the leading edge of a tooth (a rising

mechanical edge, as detected by the IC) passes the package face.

In this configuration, the device output switches to its high polar-

ity when a tooth is the target feature nearest to the package. 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 nearest to the package.

Figure 1: Relative Motion of the Target

Relative Motion of the Target is Detected by the Dual

Hall Elements

in the Hall IC.

Figure 2: Left-to-Right Direction of Target Rotation

This left-to-right (pin 1 to pin 4) direction of target rotation results

in a high output state when a tooth of the target gear is nearest the

package face (see figure 3). A right-to-left (pin 4 to pin 1) rotation

inverts the output signal polarity.

Figure 3: Magnetic Profile

The magnetic profile reflects the geometry of the target, allowing the

ATS468 to present an accurate digital output response.

On

Off

Off

On

Device Internal Switch State

Device Orientation to Target

Mechanical Position (Target movement pin 1 to pin 4)

Target

(Gear)

(Package Top View)

Sensor Branded Face

Pin 1 Side

Pin 4 Side

Branded Face

Hall Element Pitch

Target Magnetic Profile

+B

This tooth sensed earlier

This tooth sensed

later

IC

Back-Biasing

Permanent Magnet Pellet

Rotating Target

Branded Face

of Sensor

Pin 1

Pin 4

Target (Gear)

Permanent

Magnet Pellet

South Pole

North Pole

Case

(Pin 1 Side)

(Pin 4 Side)

Hall IC

Pole Piece

Element Pitch

(Concentrator)

Dual-Element

Hall Effect Device

Hall Element 1

Hall Element 2

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