ATS605LSG datasheet(11/17 Pages) ALLEGRO

11 / 17 page

Dual Output Differential

Speed and Direction Sensor IC

ATS605LSG

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Start Mode Hysteresis

This feature helps to ensure optimal self-calibration by reject-

ing electrical noise and low-amplitude target vibration during

initialization. This prevents AGC from calibrating the IC on such

spurious signals. Calibration can be performed using the actual

target features.

A typical scenario is shown in Figure 8. The Start Mode Hyster-

esis, POHYS, is a minimum level of the peak-to-peak amplitude

of the internal analog electrical signal, VPROC, that must be

exceeded before the ATS605 starts to compute switchpoints.

Figure 8: Operation of Start Mode Hysteresis

• At power-on (position 1), the ATS605 begins sampling VPROC.

• At the point where the Start Mode Hysteresis, POHYS, is exceeded, the device establishes an initial switching threshold, by using the

Continuous Update algorithm. If VPROC is falling through the limit on the low side (position 2), the switchpoint is BRP, and if VPROC

is rising through the limit on the high side (position 4), it is BOP. After this point, Start Mode Hysteresis is no longer a consider-

ation. Note that a valid VPROC value exceeding the Start Mode Hysteresis can be generated either by a legitimate target feature or by

excessive vibration.

• In either case, because the switchpoint is immediately passed as soon as it is established, the ATS605 enables switching:

--If on the low side, at BRP (position 2) the output would switch from low to high. However, because output is already high, no

output switching occurs.

At the next switchpoint, where BOP is passed (position 3), the output switches from high to low.

--If on the high side, at BOP (position 4) the output switches from high to low.

As this example demonstrates, initial output switching occurs with the same polarity, regardless of whether the Start Mode Hysteresis

is exceeded on the high side or on the low side

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