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A1214 Datasheet(PDF) 8 Page - Allegro MicroSystems |
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A1214 Datasheet(HTML) 8 Page - Allegro MicroSystems |
8 / 12 page 8 A1210-DS Worcester, Massachusetts 01615-0036 (508) 853-5000 115 Northeast Cutoff, Box 15036 www.allegromicro.com Allegro MicroSystems, Inc. Continuous-Time Latch Family A1210, A1211, A1212, A1213, and A1214 Functional Description 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). Notice that the device latches; that is, a south pole of sufficient strength towards the branded surface of the device turns the device on, and the device remains on with removal of the south pole. 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-on the device in the hysteresis range, less than BOP and higher than BRP, allows an indeterminate output state. The correct state is attained after the first excursion beyond BOP or BRP. CONTINUOUS-TIME BENEFITS Continuous-time devices, such as the A121x family, offer the fastest available power-on settling time and frequency response. Due to offsets generated during the IC packaging process, continuous-time devices typically require programming after packaging to tighten magnetic parameter distributions. In con- trast, chopper-stabilized switches employ an offset cancellation technique on the chip that eliminates these offsets without the need for after-packaging programming. The tradeoff is a longer settling time and reduced frequency response as a result of the chopper-stabilization offset cancellation algorithm. The choice between continuous-time and chopper-stabilized designs is solely determined by the application. Battery manage- ment is an example where continuous-time is often required. In these applications, VCC is chopped with a very small duty cycle in order to conserve power (refer to figure 2). The duty cycle is controlled by the power-on time, tPO, of the device. Because continuous-time devices have the shorter power-on time, they are the clear choice for such applications. For more information on the chopper stabilization technique, refer to 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. Figure 1. Switching Behavior of Latches. On the horizontal axis, the B+ direction indicates increasing south polarity magnetic field strength, and the B– direction indicates decreasing south polarity field strength (including the case of increasing north polarity). This behavior can be exhibited when using a circuit such as that shown in Panel B. BHYS VCC VOUT(SAT) B+ B– V+ 0 0 (A) (B) VCC VS Sensor Output GND VOUT RL A121x |
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