Linear Hall-Effect Sensor ICs with Analog Output

Available in a Miniature, Low Profile Surface Mount Package

A1388 and

A1389

9

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

A1388

A1389

VOUT

GND

0.1

5 V

µF

VCC

4.7 nF

Application Information

Figure 5. Typical Application Circuit

Figure 6. Chopper Stabilization Technique

Chopper Stabilization Technique

When using Hall-effect technology, a limiting factor for

switchpoint accuracy is the small signal voltage developed across

the Hall element. This voltage is disproportionally small relative

to the offset that can be produced at the output of the Hall sensor

IC. This makes it difficult to process the signal while maintain-

ing an accurate, reliable output over the specified operating

temperature and voltage ranges. Chopper stabilization is a unique

approach used to minimize Hall offset on the chip. Allegro

employs a patented technique to remove key sources of the out-

put drift induced by thermal and mechanical stresses. This offset

reduction technique is based on a signal modulation-demodula-

tion process. The undesired offset signal is separated from the

magnetic field-induced signal in the frequency domain, through

modulation. The subsequent demodulation acts as a modulation

process for the offset, causing the magnetic field-induced signal

to recover its original spectrum at base band, while the DC offset

becomes a high-frequency signal. The magnetic-sourced signal

then can pass through a low-pass filter, while the modulated DC

offset is suppressed. In addition to the removal of the thermal and

mechanical stress related offset, this novel technique also reduces

the amount of thermal noise in the Hall sensor IC while com-

pletely removing the modulated residue resulting from the chop-

per operation. The chopper stabilization technique uses a high

frequency sampling clock. For demodulation process, a sample

and hold technique is used. This high-frequency operation allows

a greater sampling rate, which results in higher accuracy and

faster signal-processing capability. This approach desensitizes

the chip to the effects of thermal and mechanical stresses, and

produces devices that have extremely stable quiescent Hall output

voltages and precise recoverability after temperature cycling.

This technique is made possible through the use of a BiCMOS

process, which allows the use of low-offset, low-noise amplifiers

in combination with high-density logic integration and sample-

and-hold circuits.

Amp

Regulator

Clock/Logic

Hall Element

Tuned

Filter

Anti-aliasing

LP Filter