ATS685LSH datasheet(10/15 Pages) ALLEGRO

10 / 15 page

Two-Wire, Zero Speed

Differential Gear Tooth Sensor IC

ATS685LSH

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,

ICC(High). When power (VCC > VCC (min)) is applied to the

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

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

power-on in the high current state, ICC(High).

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, CALI. However, this period allows the device to optimize

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-

tity required in the CALI period.

Figure 6. 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 IC in the direction indicated (from pin 1 to pin 4) and the voltage output is configured for low-side sensing, VOUT(Low). 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 when fOP ≤ 200 Hz, and more may be required at greater speeds.

Target

(Gear)

ICC

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

Start Mode

Hysteresis

Overcome

Start Mode

Hysteresis

Overcome

Start Mode

Hysteresis

Overcome

Start Mode

Hysteresis

Overcome

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