3425

DUAL, CHOPPER-STABILIZED,

ULTRA-SENSITIVE,

BIPOLAR HALL-EFFECT SWITCH

www.allegromicro.com

7

FUNCTIONAL DESCRIPTION

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 repeatability.

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 mismatch-

ing of the resistors by changing the direction of the current

flowing through the Hall plate and Hall voltage measure-

ment 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.

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. The output of these devices switches low

(turns on) when a magnetic field perpendicular to the Hall

turn-on, the output is capable of sinking 30 mA and the

switches high (turns off). Note especially that release can

occur when the magnetic field is removed but to ensure

release, a field reversal is required. The difference in the

of the device. This built-in hysteresis allows clean

switching of the output even in the presence of external

mechanical vibration and electrical noise.

Dwg. EH-012

REG

X

+V

HALL

VOLTAGE

B

+

—

Dwg. AH-011-2

0

+B

0

FLUX DENSITY

Dwg. GH-034-5

-B

RP

B

CC

V

OP

B

+V