High Accuracy GMR Wheel Speed and Direction Sensor IC

A19350

7

Allegro MicroSystems, LLC

955 Perimeter Road

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

www.allegromicro.com

FUNCTIONAL DESCRIPTION

The A19350 sensor IC contains a single-chip GMR circuit that uses

spaced elements. These elements are used in differential pairs to

provide electrical signals containing information regarding edge

position and direction of rotation. The A19350 is intended for use

with ring magnet targets as shown in Figure 8. The IC detects the

peaks of the magnetic signals and sets dynamic thresholds based on

these detected signals.

Data Protocol Description

When a target passes in front of the device (opposite the branded

face of the package case), the A19350 generates an output pulse

for each magnetic pole-pair of the target. Speed information is

provided by the output pulse rate, while direction of target rota-

tion is provided by the duration of the output pulses. The sensor

IC can sense target movement in both the forward and reverse

directions.

Forward Rotation. For the -Fxx variant, when the target is

rotating such that a target feature passes from pin 1 to pin 2, this

is referred to as forward rotation. This direction of rotation is indi-

forward direction is indicated for target rotation from pin 2 to 1.

Reverse Rotation. For the -Fxx variant, when the target is

rotating such that a target feature passes from pin 2 to pin 1, this is

referred to as reverse rotation. This direction of rotation is indi-

reverse direction is indicated for target rotation from pin 1 to 2.

Figure 7: Package Orientation

Bx

Bz

By

Pin 1

Figure 8: Parallel Orientation

Rotation

Pin 1

Device Orientation to Target

IC

E4

E2 E1

(Pin 1 Side)

(Pin 2 Side)

Package Case Branded Face

Target Magnetic Profile

+B

–B

Mechanical Position (Target moves past device pin 1 to pin 2)

S

N

N

Target

(Radial Ring Magnet)

This pole

sensed earlier

This pole

sensed later

(Top View of

Package Case)

Channel

Element Pitch

Channel B

Channel A

Channel B

Channel A

Channel B

Element Pitch

Channel A

Element Pitch

E3

N

Detected Channel Switching

Output (pulse protocol)

S

N

N

Figure 9: Basic Operation