High-Accuracy, Pulse-Width or AK Protocol

Hall-Effect Wheel Speed and Direction Sensor IC

A19302

9

Allegro MicroSystems

955 Perimeter Road

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

www.allegromicro.com

FUNCTIONAL DESCRIPTION

The A19302 sensor IC contains a single-chip Hall-effect circuit

that supports three Hall elements. These elements are used in

differential pairs to provide electrical signals containing informa-

tion regarding edge position and direction of target rotation. The

A19302 is intended for use with ring magnet targets, or, when

back-biased with an appropriate magnet, with ferromagnetic

targets. The IC detects the peaks of the magnetic signals and

sets dynamic thresholds based on these detected signals. Output

events are triggered when BDIFF transitions through the switch

points.

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 indicated on the output by

the AK or PW protocol. For the –Rxx variant, forward direction is

indicated for target rotation from pin 2 to 1 (refer to Figure 8).

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 rota-

tion. This direction of rotation is indicated on the output by the AK

or PW protocol. For the –Rxx variant, reverse direction is indicated

for target rotation from pin 1 to 2.

AK PROTOCOL DESCRIPTION

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

face of the package case), the A19302 generates an AK word for

each magnetic pole or for each tooth and each valley of the target.

Speed information is provided by the output pulse rate, while

direction of target rotation is provided in the AK data bits.

PW PROTOCOL DESCRIPTION

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

face of the package case), the A19302 generates an output pulse

for each magnetic pole or for each tooth and each valley of the

target. Speed information is provided by the output pulse rate,

while direction of target rotation is provided by the duration of

the output pulses.

Figure 8: Target Orientation Relative to Device

(ring magnet shown).

N

N

N

N

N

S

S

S

S

S

N

N

N

N

N

S

S

S

S

S

(A) Forward Rotation (-F variant)

(B) Reverse Rotation (-F variant)

Branded Face

of Sensor

Branded Face

of Sensor

Pin 1

Pin 2

Pin 1

Pin 2

Rotating Target

Rotating Target

Figure 9: Output Timing Example