ATS625LSG datasheet(14/21 Pages) ALLEGRO

14 / 21 page

True Zero-Speed Low-Jitter High Accuracy

Gear Tooth Sensor

ATS625LSG

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

www.allegromicro.com

SWITCHPOINTS

Switchpoints in the ATS625 are a percentage of the amplitude of

the signal, VPROC, after normalization with AGC. In operation,

the actual switching levels are determined dynamically. Two

DACs track the peaks of VPROC (see the Update subsection).

The switching thresholds are established at 40% and 60% of the

values held in the two DACs. The proximity of the thresholds

near the 50% level ensures the most accurate and consistent

switching, because it is where the slope of VPROC is steepest and

least affected by air gap variation.

The low hysteresis, 20%, provides high performance over vari-

ous air gaps and immunity to false switching on noise, vibration,

backlash, or other transient events.

Figure 8 graphically demonstrates the establishment of the

switching threshold levels.Because the thresholds are established

dynamically as a percentage of the peak-to-peak signal, the

effect of a baseline shift is minimized. As a result, the effects of

offsets induced by tilted or off-center installation are minimized.

UPDATE

The ATS625 incorporates an algorithm that continuously moni-

tors the system and updates the switching thresholds accordingly.

The switchpoint for each edge is determined by the signal result-

ing from the previous two edges. Because variations are tracked

in real time, the sensor has high immunity to target run-out and

retains excellent accuracy and functionality in the presence of

both run-out and transient mechanical events. Figure 9 shows

how the sensor uses historical data to provide the switching

threshold for a given edge.

Switching Threshold Levels

At Constant V

PROC

Level

100

BOP

V+

BRP

Off

Figure 8. Switchpoint Relationship to Thresholds.The device switches

when VPROC passes a threshold level, BOP or BRP, while changing in the

corresponding direction: increasing for a BOP switchpoint, and decreasing

for a BRP switchpoint.

Figure 9. Switchpoint Determination. The two previous VPROC peaks are

used to determine the next threshold level: panel A, operate point, and

panel B, release point.

Dynamic BOP Threshold Determination

Dynamic BRP Threshold Determination

100

BOP

V+

Off

100

V+

BRP

Off

(A)

(B)

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