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A1221LUA-T Datasheet(PDF) 11 Page - Allegro MicroSystems |
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A1221LUA-T Datasheet(HTML) 11 Page - Allegro MicroSystems |
11 / 16 page Chopper-Stabilized Precision Hall-Effect Latches A1220, A1221, A1222, and A1223 11 Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com Amp Regulator Clock/Logic Hall Element Low-Pass Filter 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 ele- ment. This makes it difficult to process the signal while main- taining an accurate, reliable output over the specified operating temperature and voltage ranges. Chopperstabilizationisauniqueapproachusedtominimize Halloffsetonthechip.ThepatentedAllegrotechnique,namely DynamicQuadratureOffsetCancellation,removeskeysources of the output drift induced by thermal and mechanical stresses. Thisoffsetreductiontechniqueisbasedonasignalmodulation- demodulation process. The undesired offset signal is separated fromthemagneticfield-inducedsignalinthefrequencydomain, throughmodulation.Thesubsequentdemodulationactsasa modulation process for the offset, causing the magnetic field induced signal to recover its original spectrum at baseband, while thedcoffsetbecomesahigh-frequencysignal.Themagnetic sourced signal then can pass through a low-pass filter, while the modulated DC offset is suppressed. This configuration is illus- trated in figure 2. Thechopperstabilizationtechniqueusesa400kHzhighfre- quencyclock.Fordemodulationprocess,asampleandhold techniqueisused,wherethesamplingisperformedattwicethe chopperfrequency(800kHz).Thishigh-frequencyoperation allows a greater sampling rate, which results in higher accuracy and faster signal-processing capability. This approach desensi- tizes the chip to the effects of thermal and mechanical stresses, andproducesdevicesthathaveextremelystablequiescentHall output voltages and precise recoverability after temperature cycling.Thistechniqueismadepossiblethroughtheuseofa BiCMOS process, which allows the use of low-offset, low-noise amplifiers in combination with high-density logic integration and sample-and-hold circuits. The repeatability of magnetic field-induced switching is affected slightlybyachoppertechnique.However,theAllegrohigh frequencychoppingapproachminimizestheaffectofjitterand makes it imperceptible in most applications. Applications that are morelikelytobesensitivetosuchdegradationarethoserequiring precise sensing of alternating magnetic fields; for example, speed sensing of ring-magnet targets. For such applications, Allegro recommends its digital device families with lower sensitivity tojitter.Formoreinformationonthosedevices,contactyour Allegro sales representative. Figure 2. Model of chopper stabilization technique |
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