A1425

A1425a-DS

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

115 Northeast Cutoff, Box 15036

www.allegromicro.com

Allegro MicroSystems, Inc.

• Senses motion of ring magnet or ferrous targets

• Integrated filter capacitor

• Wide operating temperature range

•

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

• Resistant to EMI

• 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

The A1425 ac-coupled Hall-effect sensor is a monolithic integrated circuit that

switches in response to changing differential magnetic fields created by rotating

ring magnets and, when coupled with a magnet, by ferrous targets. The device is

a true zero-crossing detector: the output switches precisely when the difference in

magnetic field strength between the two Hall elements is zero. A unique dual-com-

parator scheme provides for accurate switching at the zero crossing on both the

positive and negative-going regions of the differential signal, while utilizing hys-

teresis to prevent false switching. The zero-crossing nature of this device provides

excellent repeatability and accuracy for crankshaft applications.

Changes in field strength at the device face, which are induced by a moving

target, are sensed by the two integrated Hall transducers. The transducers generate

signals that are differentially amplified by on-chip electronics. This differential

sensing design provides immunity to radial vibration within the operating air gap

range of the A1425, by rejection of the common mode signal. Steady-state magnet

and system offsets are eliminated using an on-chip differential band-pass filter.

This filter also provides 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

frequencies over a wide range of air gaps and temperatures.

Each Hall effect digital integrated circuit includes a voltage regulator, two Hall

effect sensing elements, temperature compensating circuitry, a low-level amplifier,

band-pass filter, Schmitt trigger, and an output driver, which requires a pull-up

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

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

response range of the sensor, and is compatible with both TTL and CMOS logic

circuits.

The device is packaged in a 4-pin plastic SIP. The lead (Pb) free version (suffix

–T) has a 100% matte tin plated leadframe.

ABSOLUTE MAXIMUM RATINGS

Operating Temperature

*Refer to Power Derating section.

Package K, 4-pin SIP

Features and Benefits

1 2 3 4

High Accuracy Analog Speed Sensor with Integrated Filter Capacitor

and Dual Zero-Crossing Output Signal

1. VCC

2. VOUT

3. TEST

4. GND