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A1182LLHLT-T Datasheet(PDF) 9 Page - Allegro MicroSystems |
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A1182LLHLT-T Datasheet(HTML) 9 Page - Allegro MicroSystems |
9 / 16 page 9 A1180-DS, Rev. 2 Worcester, Massachusetts 01615-0036 (508) 853-5000 115 Northeast Cutoff, Box 15036 www.allegromicro.com Allegro MicroSystems, Inc. Sensitive Two-Wire Field-Programmable Chopper-Stabilized Unipolar Hall Effect Switches A1180/81/82/83 Figure 2. Chopper stabilization circuit (dynamic quadrature offset cancellation) Amp Regulator Clock/Logic Hall Element Low-Pass Filter Chopper Stabilization Technique A limiting factor for switchpoint accuracy when using Hall effect technology is the small signal voltage developed across the Hall element. This voltage is proportionally small relative to the offset that can be produced at the output of the Hall sensor device. This makes it difficult to process the signal and maintain an accurate, reliable output over the specified temperature and voltage range. Chopper stabilization is a unique approach used to minimize Hall offset on the chip. The Allegro patented technique, dynamic quadrature offset cancellation, removes key sources of the output drift induced by temperature and package stress. This offset reduction technique is based on a signal modulation-demodula- tion process. The undesired offset signal is separated from the magnetically induced signal in the frequency domain through modulation. The subsequent demodulation acts as a modulation process for the offset causing the magnetically induced signal to recover its original spectrum at base band while the dc offset becomes a high frequency signal. Then, using a low-pass filter, the signal passes while the modulated dc offset is suppressed. The chopper stabilization technique uses a 200 kHz high fre- quency clock. For demodulation process, a sample-and-hold technique is used, where the sampling is performed at twice the chopper frequency (400KHz). The sampling demodulation process produces higher accuracy and faster signal processing capability. Using this chopper stabilization approach, the chip is desensitized to the effects of temperature and stress. This tech- nique produces devices that have an extremely stable quiescent Hall output voltage, is immune to thermal stress, and has precise recoverability after temperature cycling. This technique is made possible through the use of a BiCMOS process which allows the use of low-offset and low-noise amplifiers in combination with high-density logic integration and sample-and-hold circuits. The repeatability of switching with a magnetic field is slightly affected using a chopper technique. The Allegro high frequency chopping approach minimizes the affect of jitter and makes it imperceptible in most applications. Applications that may notice the degradation are those that require the precise sensing of alter- nating magnetic fields such as ring magnet speed sensing. For those applications, Allegro recommends the “low jitter” family of digital sensors. |
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