A1421, A1422, A1423

A1421

a-DS

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

115 Northeast Cutoff, Box 15036

www.allegromicro.com

Allegro MicroSystems, Inc.

ABSOLUTE MAXIMUM RATINGS

Operating Temperature

*Refer to Power Derating section.

High Precision Hall Effect AC-Coupled Differential Sensor

with Integrated Filter Capacitor

Package K, 4-pin SIP

Features and Benefits

• Integrated tracking capacitor

• Senses motion of ring magnet or ferrous targets

• Wide operating temperature range

• Operation with magnetic input signal frequency from 20 Hz to 30 kHz

• EMI/ESD-resistant

• Large effective air gaps

• 4.0 to 26.5 V supply operating range

• Output compatible with both TTL and CMOS logic families

• Reverse battery protection

• Resistant to mechanical and thermal stress

• Accurate true zero crossing switchpoint (A1421 only)

• High vibration immunity, in running mode (A1423 only)

1. VCC

2. VOUT

3. TEST

4. GND

1234

The A1421, A1422 and A1423 are ac-coupled Hall-effect sensors which include

monolithic integrated circuits that switch in response to changing differential

magnetic fields created by rotating ring magnets or, when coupled with a magnet,

by ferrous targets. This family of devices also includes an integrated capacitor that

provides the high accuracy of analog sensing without an external filter capacitor.

This reduces cost and components, while improving the reliability of the final sen-

sor solution.

Magnetic field changes are sensed by two integrated Hall transducers and then

are differentially amplified on the chip. Differential sensing provides immunity to

radial vibration, within the device operating air gap range, by rejection of this

common-mode signal change. Steady-state system offsets are eliminated using an

on-chip differential bandpass filter with integrated capacitor. This filter also pro-

vides relative immunity to interference from electromagnetic sources. The device

utilizes advanced temperature compensation for the high-pass filter, sensitivity,

and Schmitt trigger switchpoints to guarantee optimal operation to low frequen-

cies over a wide range of air gaps and temperatures.

Each device includes: a voltage regulator, two Hall transducers, temperature com-

pensating circuitry, a low-level amplifier, bandpass filter, Schmitt trigger, and an

output driver. The on-board regulator permits operation with supply voltages from

4.0 to 26.5 V. The output stage can switch 20 mA over the full frequency response

range of the sensor, and is compatible with TTL and CMOS logic circuits.

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