2-WIRE,

CHOPPER-STABILIZED,

HALL-EFFECT SWITCHES

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7

FUNCTIONAL DESCRIPTION

Dwg. EH-012

REG

X

+V

HALL

VOLTAGE

B

+

—

Dwg. AH-011-2

100

Ω

Dwg. EH-011-2A

0.1

µF

SUPPLY

X

'UA' PACKAGE

0.95 V

–

+

Chopper-Stabilized Technique. 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. 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 dependen-

cies, and thermal stress. The chopper-stabilizing technique

cancels the mismatching of the resistor circuit by changing the

direction of the current flowing through the Hall plate using

CMOS switches and Hall voltage measurement taps, while

maintaing the Hall-voltage signal that is induced by the external

magnetic flux. The signal is then captured by a sample-and-

hold circuit and further processed using low-offset bipolar

circuitry. 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 repeatability. A relatively high sampling frequency is

used in order that faster signals can be processed.

More detailed descriptions of the circuit operation can be

found in: Technical Paper STP 97-10, Monolithic Magnetic

Hall Sensor Using Dynamic Quadrature Offset Cancellation

and Technical Paper STP 99-1, Chopper-Stabilized Amplifiers

With A Track-and-Hold Signal Demodulator.

Operation. As shown in the output characteristic graphs, the

output of the A3362 turns on when a magnetic field (south pole)

perpendicular to the Hall sensor is increased above the operate

current equal to the device operating current plus a current

current equal only to the Hall-effect sensor operating current

hysteresis allows clean switching of the output even in the

presence of external mechanical vibration or 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.

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