GMR Speed and Direction Crankshaft Sensor

with Three-Wire, Pulse-Width Output

ATS16951PSM

9

Allegro MicroSystems

955 Perimeter Road

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

www.allegromicro.com

FUNCTIONAL DESCRIPTION

Sensing Technology

The ATS16951PSM contains two GMR bridge elements that

provide an electrical output signal containing information regard-

ing target edge position and—if Pulse Width Protocol optioned—

direction of rotation.

Target Profiling

After proper power is applied to the ATS16951PSM, digital infor-

mation—representative of the mechanical features of a rotating

target—will be available at the OUT pin. The waveform diagram

in Figure 8 shows the translation of the induced magnetic profile

to a digital speed and direction signal. The two digital signals are

used to determine the location of the switching feature as well as

the direction of rotation.

Figure 8: Magnetic Profile

If the device is set on option M1 (switch in the middle of the

target feature), the output pulse is based on the 50% of the speed

channel.

If the device is set on option M2 (switch on the mechanical edge

of the target), the output pulse is based on the 50% of the Dir

channel.

Switch Points

The ATS16951PSM switch points are established dynamically as a

percentage of the internal VPROC signal amplitude (see Figure 5) to

minimize the signal shift effect. This is accomplished by inde-

pendently tracking the speed and direction peaks of each VPROC

channel, where the switching thresholds are established at fixed

percentages of the two tracking signals.

Output switching threshold percentage on the speed channel is

programmable to ensure the most accurate and consistent output

switching. Additionally, the dynamic switch point thresholds

allow the ATS16951PSM to properly detect direction of rota-

tion when used with targets containing signature regions. A 50%

threshold is recommended for standard crank targets, while the

other programmable options allow for functionality on targets

with different mechanical geometries.

Sensor Output Protocol

If Pulse Width Protocol optioned, the ATS16951PSM compares

the relative amplitude values of the two GMR bridges to deter-

mine which direction the target is rotating. The direction of rota-

tion is then communicated through the output pulse width. While

in calibration mode, direction information is not available. As a

result of this, forward output pulses (tW(FWD)) are always given,

independent of the true target rotation direction.

If speed only is programmed (Option O), no direction infor-

mation is available. Only forward output pulses (tW(FWD)) are

produced.

NOTE: For proper functionality, the output must be programmed

such that the signature region is a non-switching feature (see

Application Information section).

Forward Pulse Rotation Direction

The ATS16951PSM can be programmed such that the output will

provide forward pulses (tW(FWD)) when the target rotation is from

pin 1 to pin 3 (Option F) or from pin 3 to pin 1 (Option R). This

is illustrated in Figure 9 with the arrow on the target indicating

direction of rotation.