A3280(2010) 查看數據表（PDF） - Allegro MicroSystems

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A3280
(Rev.:2010)

Chopper-Stabilized, Precision Hall-Effect Latches

Allegro MicroSystems 

A3280, A3281

and A3283

Chopper-Stabilized, Precision

Hall-Effect Latches

FUNCTIONAL DESCRIPTION

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 cancel-

lation 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. 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

Sensing 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 element

exceeds the operate point threshold (BOP). After turn-on, the

output is capable of sinking 25 mA and the output voltage is

VOUT(SAT). Note that the device latches; that is, a south pole of

sufficient strength towards the branded surface of the device

will turn the device on; removal of the south pole will leave the

device on. When the magnetic field is reduced below the release

point (BRP), the device output goes high (turns off). The differ-

ence in the magnetic operate and release points is the hysteresis

(Bhys) of the device. This built-in hysteresis allows clean switch-

ing of the output even in the presence of external mechanical

vibration and electrical noise.

Powering up in the absence of a magnetic field (less than

BOP and higher than BRP) will allow an indeterminate output

state. The correct state is warranted after the first excursion

beyond BOP or BRP.

It is strongly recommended that an external bypass capacitor

Allegro MicroSystems, Inc.

8

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

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