11

ATS643-DS, Rev. 1

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

115 Northeast Cutoff, Box 15036

www.allegromicro.com

Allegro MicroSystems, Inc.

Self-Calibrating, Zero-Speed Differential GTS with Continuous Update

ATS643LSH

Power-On State Operation. The ATS643 is guaranteed to

Initial Edge Detection. The device self-calibrates using the

initial teeth sensed, and then enters Running mode. This results

in reduced accuracy for a brief period (less than four teeth),

however, it allows the device to optimize for continuous update

yielding adaptive sensing during Running mode. As shown in

figure 5, the first three high peak signals are used to calibrate

AGC. However, there is a slight variance in the duration of ini-

tialization, depending on what target feature is nearest the sensor

when power-on occurs.

Figure 5. Power-on initial edge detection. This figure demonstrates four typical power-on scenarios. All of these examples assume that the target is

moving relative to the sensor in the direction indicated. The length of time required to overcome Start Mode Hysteresis, as well as the combined effect

of whether it is overcome in a positive or negative direction plus whether the next edge is in that same or opposite polarity, affect the point in time when

AGC calibration begins. Three high peaks are always required for AGC calibration.

Target

(Gear)

Output

Output

Output

Output

Power-on

over valley

Power-on

at rising edge

Power-on

over tooth

Power-on

at falling edge

AGC Calibration

Running Mode

AGC Calibration

Running Mode

AGC Calibration

Running Mode

AGC Calibration

Running Mode

Sensor Position

1

3 4

2

1

2

4

3

Start Mode

Hysteresis

Overcome

Start Mode

Hysteresis

Overcome

Start Mode

Hysteresis

Overcome

Start Mode

Hysteresis

Overcome