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3283 Datasheet(PDF) 7 Page - Allegro MicroSystems |
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3283 Datasheet(HTML) 7 Page - Allegro MicroSystems |
7 / 11 page 3280, 3281, AND 3283 CHOPPER-STABILIZED, PRECISION HALL-EFFECT LATCHES www.allegromicro.com 7 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 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 dependen- cies, 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 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 sensor 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 difference in the magnetic operate and release points is the hysteresis (Bhys) of the device. This built-in hysteresis allows clean switching 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. 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 VOUT(SAT) CC V OP B +V |
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