A1645LK-I2【PDF 9/14 页】IC SENSOR HALL EFFECT AC 4-SIP

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Two-Wire True Zero-Speed Miniature Differential

Peak-Detecting Sensor IC with Continuous Calibration

A1642

Allegro MicroSystems, LLC

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-

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

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

the device 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,

compensating for offset drift. Continuous operation also allows

it to compensate for offsets induced by temperature variations

over time.

Digital Peak Detection

A digital DAC tracks the internal analog voltage signal V

PROC

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

signal. In the example shown in gure 6, the DAC would rst

track up with the signal and hold the upper peaks value. When

PROC

drops below this peak value by B

, the device hyster-

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

the signal downward toward the negative V

PROC

peak. Once the

DAC acquires the negative peak, the output will again switch

states when V

PROC

is greater than the peak by the value B

. At

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

digital tracking of the differential analog signal allows the device

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, as

shown in the lowest panel.

Small

Large

Small

Large

Internal Differential

Analog Signal

Response, with AGC

Internal Differential

Analog Signal

Response, without AGC

V+

Target

Ring Magnet

Figure 6: Peak Detecting Switchpoint Detail

Device

Output Current

Internal

Differential

Analog Signal

V+

I+

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