8

A3245-DS, Rev. 1

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

115 Northeast Cutoff, Box 15036

www.allegromicro.com

Allegro MicroSystems, Inc.

Chopper-Stabilized Omnipolar Hall Effect Switches

A3245

Functional Description

B+

B–

V+

0

0

VCC

Sensor Output

GND

VOUT

A3245

0.1 μF

Operation

The output of this device switches low (turns on) when a mag-

netic field perpendicular to the Hall sensor exceeds the operate

minimum of 30 mA. When the magnetic field is reduced below

output switches high (turns off). The difference in the magnetic

This built-in hysteresis allows clean switching of the output even

in the presence of external mechanical vibration and electrical

noise.

Applications

It is strongly recommended that an external bypass capacitor be

connected (in close proximity to the Hall sensor) between the

supply and ground of the device to reduce both external noise

and noise generated by the chopper stabilization technique. As is

shown in Panel B of figure 1, a 0.1μF capacitor is typical.

Omnipolar switches allow operation with either a north pole or

south pole magnet orientation, enhancing product manufactur-

ability with the device.

Extensive applications information on magnets and Hall-effect

sensors is available in:

• Hall-Effect IC Applications Guide, AN27701,

• Hall-Effect Devices: Gluing, Potting, Encapsulating, Lead

Welding and Lead Forming, AN27703.1

• Soldering Methods for Allegro’s Products – SMT and Through-

Hole, AN26009

All are provided in Allegro Electronic Data Book, AMS-702 and

the Allegro Web site: www.allegromicro.com

Figure 1: Switching Behavior of Omnipolar Switches.

In Panel A, on the horizontal axis, the B+ direction indicates increasing south polarity

magnetic field strength, and the B– direction indicates decreasing south polarity field strength (including the case of increasing north

polarity). This behavior can be exhibited when using a circuit such as that shown in panel B.

(A)

(B)