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A1421-DS

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

115 Northeast Cutoff, Box 15036

www.allegromicro.com

Allegro MicroSystems, Inc.

High Precision Hall Effect AC-Coupled Differential Sensor with Integrated Filter Capacitor

A1421, A1422, A1423

Applications Information

The A1421, A1422, and A1423 are versatile high-precision dif-

ferential sensors that can be used in a wide range of applications.

Proper choice of the target material and shape, magnet material

and shape, and assembly techniques enables large working air

gaps and high switchpoint accuracy over the device operating

temperature range.

Sensor Operation

The device sensor IC contains two integrated Hall transducers

that are used to differentially sense a magnetic field across the

surface of the IC. Referring to figure 1, which shows curves

for the A1421 as an example, the trigger switches the output

increasing in strength (referred to as the positive direction). In

the example, the A1421 output voltage switches high (off), and

switches the output low (on) when the differential magnetic field

The operation is achieved through the use of two separate com-

ential signal. The hysteresis on each comparator precludes false

switching on noise or target jitter.

The behavior is similar for the A1422 and the A1423. The switch-

points are as shown in the magnetic charactersitics table, and the

output polarity is inverted. This is illustrated in figure 2, on the

next page.

Start-up

Delay

Figure 1. Typical output characteristics with dual comparator operation. The example shown is for the A1421. Characteristics

shown without delay, see characteristic data charts for delay and phase shift contributions.

On

Off

Off

1421 Switching State

Applied Magnetic

Comparator 1, A1421

Comparator 2, A1421

A

0.0

15.0