True Zero-Speed, High Accuracy, Ring Magnet Sensor IC

A1667

7

Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A.

www.allegromicro.com

FUNCTIONAL DESCRIPTION

HALL TECHNOLOGY

The single-chip differential Hall-effect sensor IC contains two

Hall elements as shown in figure 1, which simultaneously sense

the magnetic profile of the ring magnet. The magnetic fields are

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

precise switching of the digital output signal.

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

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

proprietaryBiCMOSprocess.

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 transla-

tion of the mechanical profile, through the magnetic profile that

it induces, to the digital output signal of the A1667. 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 ring magnet and orienta-

tion 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 ring magnet configured

as shown in figure 2. That direction of rotation (of the target

side adjacent to the package face) 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 device output switching from low to high

output state as the leading edge of a north magnetic pole passes

the device face. In this configuration, the device output voltage

switches to its high polarity when a north pole is the target feature

nearest to the device. If the direction of rotation is reversed, then

the output polarity inverts.

Target

(Ring Magnet)

(Pin 1 Side)

(Pin 4 Side)

Hall IC

Element Pitch

Hall Element 1

Hall Element 2

N

N

S

S

N

N

N

N

N

N

S

S

N

N

S

S

S

S

S

S

Pin 1

Pin 1

Pin 4

Pin 4

Branded Face

of K Package

Branded Face

of L Package

Rotatin

Rotatin

g

g

T

T

arget

arget

Off

On

On

Off

Device Internal Switch State

Device Orientation to Target

(Pin 1 Side)

(Pin 4 Side)

IC

Element Pitch

Hall Element 1

Hall Element 2

Sensor Branded Face

Target Magnetic Profile

+B

–B

+t

Mechanical Position (Target moves past device pin 1 to pin 4)

N

S

S

Target

(Radial Ring Magnet)

This pole

sensed earlier

This pole

sensed later

(View of Sensor

Opposite Pins)

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

elements 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 state when a north magnetic pole of the target is nearest

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

inverts the output signal polarity.

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

the A1667 to present an accurate digital output response.