Two-Wire True Zero Speed Miniature Differential

Peak-Detecting Gear Tooth Sensor with Continuous Calibration

ATS642LSH

11

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Automatic Gain Control (AGC)

This feature allows the device to operate with an optimal internal

electrical signal, regardless of the air gap (within the AG speci-

fication). During calibration, the device determines the peak-to-

peak amplitude of the signal generated by the target. The gain of

the sensor is then automatically adjusted. Figure 5 illustrates the

effect of this feature.

Automatic Offset Adjust (AOA)

The AOA is patented circuitry that automatically compensates

for the effects of chip, magnet, and installation offsets. (For

capability, see Dynamic Offset Cancellation, in the Operat-

ing Characteristics table.) This circuitry is continuously active,

including both during calibration mode and running mode, com-

pensating for any offset drift. Continuous operation also allows it

to compensate for offsets induced by temperature variations over

time.

Digital Peak Detection

and is used for holding the peak value of the internal analog

signal. In the example shown in figure 6, the DAC would first

track up with the signal and hold the upper peak’s value. When

esis, the output would switch and the DAC would begin tracking

DAC acquires the negative peak, the output will again switch

this point, the DAC tracks up again and the cycle repeats. The

digital tracking of the differential analog signal allows the sensor

to achieve true zero-speed operation.

Figure 5. Automatic Gain Control (AGC). The AGC function corrects for

variances in the air gap. Differences in the air gap affect the magnetic

gradient, but AGC prevents that from affecting device performance, a

shown in the lowest panel.

Mechanical Profile

Internal Differential

Analog Signal

Response, with AGC

Internal Differential

Analog Signal

Response, without AGC

Ferrous Target

V+

V+

Figure 6: Peak Detecting Switchpoint Detail

Device

Output Current

Internal

Differential

Analog Signal

V+

I+