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A1250LLHLX-T Datasheet(PDF) 7 Page - Allegro MicroSystems |
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A1250LLHLX-T Datasheet(HTML) 7 Page - Allegro MicroSystems |
7 / 12 page Hall-Effect Latch / Bipolar Switch A1250 7 Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com FUNCTIONAL DESCRIPTION The output of this device switches low (turns on) when a magnetic field perpendicular to the Hall sensor IC exceeds the operate point threshold, BOP. After turn-on, the output voltage is VOUT(SAT). The output transistor is capable of sinking current up to the short circuit current limit IOM, which is a minimum of 30 mA. 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. Given the magnetic parameter specifications (refer to Magnetic Characteristics table), bipolar switches will operate in one of three modes, depending on switchpoints. For typical values of BOP and BRP, the device will operate as a latch, as shown in figure 1a. Note that, when the magnetic flux density exceeds a switchpoint, the output will retain its state when the magnetic field is removed. The other two modes of operation are the unipolar switch and the negative switch, shown in panels 1b and 1c, respectively. The unipolar switch type operates only in a south polarity field, and will switch to the high state if the magnetic field is removed. The negative switch operates only in a north polarity field, and will switch to the low state if the magnetic field is removed. Individual bipolar switch devices exhibit any one of the three switching behaviors: latch, unipolar, or negative switch. Because these devices are not guaranteed to behave as latches, magnetic fields of sufficient magnitude and alternate polarity are required to ensure output switching. Powering up the device in the hysteresis band, that is in a mag- netic field less than BOP and higher than BRP, allows an indeter- minate output state. Note that this hysteresis band encompasses zero magnetic field on devices that exhibit latch behaviors. The correct state is determined after the first magnetic excursion beyond BOP or BRP. Figure 1: Bipolar Device Output Switching Modes These behaviors can be exhibited when using a circuit such as that shown in figure 1. Panel A displays the hysteresis when a device exhibits latch mode (note that the BHYS band incorporates B = 0), panel B shows unipolar switch behavior (the BHYS band is more positive than B = 0), and panel C shows negative switch behavior (the BHYS band is more negative than B = 0). Bipolar devices, such as the A1250, can operate in any of the three modes. BHYS VOUT(SAT) V+ 0 BHYS VOUT(SAT) V+ 0 BHYS VOUT(SAT) V+ 0 VCC VCC VCC B+ B– B+ B– 0 0 B+ B– 0 (A) (B) (C) |
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