ATS625LSG datasheet(16/21 Pages) ALLEGRO

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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

ACCURACY

While the update algorithm will allow the sensor to adapt to

typical air gap variations, major changes in air gap can adversely

affect switching performance. When characterizing sensor

performance over a significant air gap range, be sure to re-power

the device at each test at different air gaps. This ensures that

self-calibration occurs for each installation condition. See the

Operating Characteristics table and the charts in the Character-

istic Data: Relative Timing Accuracy section for performance

information.

REPEATABILITY

Repeatability measurement methodology has been formulated to

minimize the effect of test system jitter on device measurements.

By triggering the measurement instrument, such as an oscillo-

scope, close to the desired output edge, the speed variations that

occur within a single revolution of the target are effectively nul-

lified. Because the trigger event occurs a very short time before

the measured event, little opportunity is given for measurement

system jitter to impact the time-based measurements.

After the data is taken on the oscilloscope, statistical analysis

of the distribution is made to quantify variability and capabil-

ity. Although complete repeatability results can be found in the

Characteristic Data: Repeatability section, figure 11 shows the

correlation between magnetic signal strength and repeatability.

Because an direct relationship exists between magnetic signal

strength and repeatability, optimum repeatability performance

can be attained through minimizing the operating air gap and

optimizing the target design.

Figure 11. Repeatability Measurement Methodology

Target Mechanical Profile

Sensor Output

Electrical Profile

(target movement

from pin 1 to pin 4)

Low Resolution Encoder

High Resolution Encoder

Oscilloscope triggers at

n events after low-resolution pulse

Statistical distribution

of 1000 sweeps

Next high-resolution encoder pulse

(at target edge)

Oscilloscope trace

of 1000 sweeps for

the same output edge

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