True Zero Speed Miniature Differential Peak-

Detecting Gear Tooth Sensor

ATS645LSH

9

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (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 cancels the

effects of chip, magnet, and installation offsets. (For capability,

see Dynamic Offset Cancellation, in the Operating Characteris-

tics table.) This circuitry is continuously active, including both

during calibration mode and running mode, compensating for

any offset drift. Continuous operation also allows it to compen-

sate 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+