True Zero-Speed Low-Jitter High Accuracy

Gear Tooth Sensor

ATS625LSG

12

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036

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

www.allegromicro.com

Sensor Operation Description

Power-On State

At power-on, the device is guaranteed to initialize in the OFF

First Edge Detection

The device uses the first two mechanical edges to synchronize

with the target features (tooth or valley) and direction of rotation

of the target. The device is synchonized by the third edge. The

actual behavior is affected by: target rotation direction relative to

the, target feature (tooth, rising edge, falling edge, or valley) that

is centered on the device at power-on, and fact that the sensor

eventual direction of target rotation. The interaction of these fac-

tors results in a number of possible power-on scenarios. These

are diagrammed in figure 6. In all start-up scenarios, the correct

number of output edges is provided, but the accuracy of the first

two edges may be compromised.

Target Mechanical Profile

(Start-up over valley)

Target Magnetic Profile

(Start-up over tooth)

(Start-up over rising edge)

(Start-up over falling edge)

Target Mechanical Profile

(Start-up over valley)

Target Magnetic Profile

(Start-up over tooth)

(Start-up over rising edge)

(Start-up over falling edge)

Sensor start-up location

Sensor start-up location

Sensor

Pin 4 Side

Sensor

Pin 1 Side

Target Motion Relative to Sensor

Sensor

Pin 1 Side

Sensor

Pin 4 Side

Target Motion Relative to Sensor

(A) Target relative movement

as shown in figure 3. Output

signal is high over the tooth.

(B) Target relative movement

opposite that shown in figure 3.

Output signal is low over the tooth.

Figure 6. Start-up Position And Relative Motion Effects on First Device Output Switching. Panel A shows the effects when the