Two-Wire, Zero-Speed

Differential Gear Tooth Sensor IC

ATS684LSN

11

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

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

The ATS684 is guaranteed to power-on in the high current state,

a short period of time is required to power the various portions of

the circuit. During this period, the ATS684 will power-on in the

Figure 7: Power-On Initial Edge Detection.

Power-On

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 3) and the voltage

output is configured for low-side

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

required at greater speeds.

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

mize for running mode operation. As shown in Figure 7, the first

three high peak signals corresponding to rising output edges are

used to calibrate AGC (Automatic Gain Control). There is a slight

variance 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