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A1469LK

Three-Wire True Zero-Speed Differential Peak-Detecting Sensor IC with Continuous Calibration

Allegro MicroSystems 

A1469

Three-Wire True Zero-Speed Differential Peak-Detecting

Sensor IC with Continuous Calibration

Automatic Gain Control (AGC)

This feature allows the device to operate with an optimal internal

electrical signal, regardless of the differential signal amplitude

(within the BDIFF and BDIFFEXT specifications). During calibra-

tion, the device determines the peak-to-peak amplitude of the

signal generated by the target. The gain of the device is then auto-

matically adjusted. Figure 4 illustrates the effect of this feature.

During running mode, the AGC continues to monitor the system

amplitude, reducing the gain if necessary; see the Device Opera-

tion section for more details.

Automatic Offset Adjust (AOA)

The AOA is patented circuitry that automatically compensates for

the effects of chip, magnet, and installation offsets. 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, VPROC,

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

signal. In the example shown in Figure 5, the DAC would first

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

VPROC drops below this peak value by BOP , the device hyster-

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

the signal downward toward the negative VPROC peak. After the

DAC acquires the negative peak, the output will again switch

states when VPROC is greater than the peak by the value BRP . 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.

Target

Ring Magnet

V+

Internal Differential

Analog Signal

Response, without AGC

V+

Internal Differential

Analog Signal

Response, with AGC

NS

NS

AGLarge

AGSmall

AGSmall

AGLarge

Figure 4: 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.

V+

Internal

Differential

Analog Signal,

VPROC

0

V–

VCC

Device Output,

VOUT

BOP

BRP

BOP

BRP

VOUT(sat)

Figure 5: Differential Signal Peaks

The peaks in the resulting differential signal are used to set the

operate (BOP ) and release (BRP ) switchpoints.

Allegro MicroSystems, LLC

10

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

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