Two-Wire, Zero Speed

Differential Gear Tooth Sensor IC

ATS685LSH

9

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

(A) TEAG varying; cases such as

eccentric mount, out-of-round region,

normal operation position shift

typically resulting in the IC

0

B

OP

B

RP

B

OP

B

RP

B

OP

B

RP

B

OP

B

RP

B

OP

B

OP

B

RP

360

Target Rotation (°)

Hysteresis Band

(Delimited by switchpoints)

V+

magnetic field for digital output

V+

Larger

TEAG

Smaller

TEAG

IC

Target

Larger

TEAG

Target

IC

Smaller

TEAG

Smaller

TEAG

Figure 5. The Continuous Update algorithm allows the Allegro IC to interpret and adapt to variances in the magnetic field generated by the target

as a result of eccentric mounting of the target, out-of-round target shape, and similar dynamic application problems that affect the TEAG (Total

Effective Air Gap). As shown in panel A, the variance in the target position results in a change in the TEAG. This affects the IC as a varying

Continuous Update of Switchpoints

Switchpoints are the threshold levels of the differential internal

density, B, induced by the target and sensed by the Hall elements.

state changes from low to high.

As shown in figure 5, threshold levels for the switchpoints are

established as a function of the peak input signal levels. The device

incorporates an algorithm that continuously monitors the input signal

and updates the switching thresholds accordingly with limited inward

by the detection of the previous two signal edges. In this manner,

variations are tracked in real time.