Self-Calibrating TPOS Gear Tooth Sensor Optimized

for Automotive Cam Sensing Applications

ATS673 and

ATS674

11

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036

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

www.allegromicro.com

AGC (Automatic Gain Control)

The AGC feature is implemented by a unique patented self-

calibrating circuitry. After each power-on, the devices measure

the peak-to-peak magnetic signal. The gain of the sensor is then

adjusted, keeping the internal signal amplitude constant over the

air gap range of the device. This feature ensures that operational

characteristics are isolated from the effects of changes in AG.

The effect of AGC is shown in figure 7.

Magnetic Flux Density Versus Target Edge Position

0

1020

30405060

708090

Target Rotation (°)

0

100

200

300

400

500

600

1.50

AG (mm):

2.00

2.50

3.00

3.50

Target Rotation (°)

Internal Analog Signal after AGC Versus Target Edge Position

0

10

203040

506070

8090

0

0.5

1.0

1.5

2.0

1.50

AG (mm):

2.00

2.50

3.00

3.50

Figure 7. Effect of AGC. The upper panel shows the magnetic gradient detected at the Hall element, with no amplification.

performance by the rest of the circuits that reference this signal.