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A1242LUA-I2-T Datasheet(PDF) 7 Page - Allegro MicroSystems |
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A1242LUA-I2-T Datasheet(HTML) 7 Page - Allegro MicroSystems |
7 / 11 page 7 A1242-DS Worcester, Massachusetts 01615-0036 (508) 853-5000 115 Northeast Cutoff, Box 15036 www.allegromicro.com Allegro MicroSystems, Inc. Two-Wire Chopper-Stabilized Hall Effect Latch A1242 Functional Description OPERATION The output, ICC, of the A1242 switches to the high current state when a magnetic field perpendicular to the Hall sensor exceeds the operate point threshold, BOP. Note that the device latches, that is, a south pole of sufficient strength towards the branded surface of the device switches the device output to ICC(H). The device retains its output state if the south pole is removed. When the magnetic field is reduced to below the release point thresh- old, BRP, the device output goes to the low current state. The dif- ference between the magnetic operate and release points is called the hysteresis of the device, BHYS. This built-in hysteresis allows clean switching of the output even in the presence of external mechanical vibration and electrical noise. . TYPICAL APPLICATION CIRCUIT The A1242 should be protected by an external bypass capaci- tor, CBYP, connected between the supply, VCC, and the ground, GND, of the device. CBYP reduces both external noise and the noise generated by the chopper-stabilization function. As shown in figure 2, a 0.01 μF capacitor is typical. Installation of CBYP must ensure that the traces that connect it to the A1242 pins are no greater than 5 mm in length. All high-frequency interferences conducted along the supply lines are passed directly to the load through CBYP, and it serves only to protect the A1242 internal circuitry. As a result, the load ECU (electronic control unit) must have sufficient protection, other than CBYP, installed in parallel with the A1242. A series resistor on the supply side, RS (not shown), in combina- tion with CBYP, creates a filter for EMI pulses. When determining the minimum VCC requirement of the A1242 device, the voltage drops across RS and the ECU sense resistor, RSENSE, must be taken into consideration. The typical value for RSENSE is approximately 100 Ω. Extensive applications information on magnets and Hall-effect sensors is available in: • Hall-Effect IC Applications Guide, AN27701, • Hall-Effect Devices: Gluing, Potting, Encapsulating, Lead Welding and Lead Forming, AN27703.1 • Soldering Methods for Allegro Products – SMD and Through-Hole, AN26009 All are provided in Allegro Electronic Data Book, AMS-702 and the Allegro Web site: www.allegromicro.com. Figure 1. Switching Behavior of the A1242. 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). BHYS ICC(H) ICC(L) B+ I+ B– 0 0 GND A1242 VCC V+ 0.01 uF A B B GND ECU Package UA Only A B Maximum separation 5 mm R SENSE C BYP Figure 2. Typical Application Circuit |
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