3150

PROGRAMMABLE, CHOPPER-

STABILIZED, PRECISION,

HALL-EFFECT SWITCH

www.allegromicro.com

FUNCTIONAL DESCRIPTION

Dwg. EH-012

REG

X

Chopper-Stabilized Technique. These devices use a

proprietary dynamic offset cancellation technique, with an

internal high-frequency clock to reduce the residual offset

voltage of the Hall element that is normally caused by device

overmolding, temperature dependencies, and thermal stress.

This technique produces devices that have an extremely stable

quiescent Hall output voltage, are immune to thermal stress, and

have precise recoverability after temperature cycling. This

technique will also slightly degrade the device output repeatabil-

ity.

The Hall element can be considered as a resistor array

similar to a Wheatstone bridge. A large portion of the offset is a

result of the mismatching of these resistors. The chopper-

stabilizing technique cancels the mismatching of the resistors by

changing the direction of the current flowing through the Hall

plate and Hall voltage measurement taps, while maintaining the

Hall-voltage signal that is induced by the external magnetic flux.

The signal is, then, captured by a sample-and-hold circuit.

Operation. The output of these devices switches low (turns

ON) when a magnetic field (south pole) perpendicular to the

Hall sensor exceeds the operate point threshold (B

turn-ON, the output is capable of sinking 25 mA and the output

voltage is V

the release point (B

The difference in the magnetic operate and release points is the

hysteresis (B

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-stabiliza-

tion technique.

The simplest form of magnet that will operate these devices

is a bar magnet with the south-seeking pole towards the branded

surface of the device. Many other methods of operation are

possible. Extensive applications information on magnets and

Hall-effect sensors is also available in the Allegro Electronic

Data Book AMS-702 or Application Note 27701, or

www.allegromicro.com

SUPPLY

OUTPUT

Dwg. EH-013

0.1

µF

SUPPLY

+V

HALL

VOLTAGE

B

+

—

Dwg. AH-011-2

+B

0

FLUX DENSITY

Dwg. GH-007-2

0

RP

B

CC

V

OP

B

+V