Two-Wire, Zero Speed

Differential Gear Tooth Sensor IC

ATS685LSH

10

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Power-On

The ATS685 is guaranteed to power-on in the high current state,

device, a short period of time is required to power the vari-

ous portions of the circuit. During this period, the ATS685 will

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

for running mode operation. As shown in figure 6, the first three

high peak signals corresponding to rising output edges are used to

calibrate AGC (Automatic Gain Control). There is a slight vari-

ance in the duration of initialization, depending on what target

feature is opposite the sensor IC when power-on occurs. Also, a

high speed of target rotation at power-on may increase the quan-

Figure 6. Power-On Initial Edge Detection. This figure demonstrates four typical power-on scenarios. All of these examples assume that the target is

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

Target

(Gear)

Power-on

opposite

tooth

Power-on

at falling

mechanical

edge

Power-on

at rising

mechanical

edge

Power-on

opposite

valley

AGC Calibration

Running Mode

AGC Calibration

Running Mode

AGC Calibration

Running Mode

AGC Calibration

Running Mode

Device

Position

1

1

4

4

2

2

3

3

Start Mode

Hysteresis

Overcome

Start Mode

Hysteresis

Overcome

Start Mode

Hysteresis

Overcome

Start Mode

Hysteresis

Overcome