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Design News, February 2013

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to a voltage. The Hall voltage is galvanically isolated from the primary current, and is dependent on the direction of the current flow, allowing for bi-directional current sensing in both AC and DC modes. The transducer is placed in the area of highest flux density to optimize the magnetic coupling. Since the die surface with the Hall element is now closest to the primary conductor, this approach optimizes transducer sensitivity and accuracy. The magnetic field generated by current flowing through a conductor is not temperature-dependent. As a result, the integrated Hall approach has one less temperature-dependent error term compared to the sense resistor and amplifier technique. The conductor resistance of integrated Hall ICs is as low as 0.6 mΩ, an order of magnitude smaller than most sense resistors employed in low-side sensing configurations. This saves power consumption in customer applications and provides a higher efficiency and more eco-friendly solution. The small footprint also saves PCB area, thereby reducing overall system cost. Table 1 compares the area and power dissipation for a 30A continuous current sense application for a sense resistor and amplifier solution, and Allegro's ACS711 QFN and ACS710 Hall effect ICs. Smart Battery Current Sensing An increasingly relevant example of a low-side current sensing implementation is charge current monitoring for smart battery systems. In addition to the [w w w. de s ig n n e w s . c o m ] figure 3: Smart battery current sensing. figure 4: Motor control current sensing. f e b r u a ry 2013 T r e n d waTch : s e ns o r s / mach ine v is io n / a s up p le me nT To de s ign news T11

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