ATS667LSG datasheet(10/14 Pages) ALLEGRO

10 / 14 page

True Zero-Speed, High Accuracy Gear Tooth Sensor IC

ATS667LSG

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

OP(initial)

RP(initial)

Start Mode

Hysteresis, POHYS

Output Signal, VOUT

If exceed PO

HYS

on high side

If exceed PO

HYS

on low side

IC Position

Relative to Target

Target Magnetic Profile

Differential Signal, VPROC

Target, Gear

Start Mode Hysteresis

This feature helps to ensure optimal self-calibration by rejecting

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 5. The Start Mode Hysteresis,

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

internal analog electrical signal, VPROC, that must be exceeded

before the ATS667 starts to compute switchpoints.

Figure 5. Operation of Start Mode Hysteresis

• At power-on (position 1), the ATS667 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 consideration. 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 it established, the ATS667 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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