Design News, February 2013

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s e n s o r s / m ac h i n e v i s i o n DESIGN APPLICATIONS New Approaches to High-Efficiency Current Sensing Integrated hall sensor ICs save power and space. by AliHuSAiN SiroHiwAlA, AllEgro MiCroSyStEMS iNC. R Recent advancements in integrated Hall-effect current sensor technology provide an alternative current sensing solution that reduces power loss, achieves most cost targets, and occupies a much smaller volume on the application printed circuit board. Current Sensing with a Sense resistor and Amplifier Conventional current sensing techniques insert a sense resistor in series with the conductor carrying the current being measured. An amplifier is also required, so that when current flows through the resistor, the voltage developed can be used to measure the input current. The value (usually ranging from 1 to 100 mΩ) of the sense resistor depends on the maximum target current that is to be sensed. Smaller sense resistor values develop a lower signal-voltage when current is applied. The resistor-amplifier sensing circuit is implemented as a shunt circuit, either on the low side (near ground potential) or on the high side (near supply potential) of the load that carries the applied current. High-side current sensing allows the detection of short-circuit conditions [w w w. de s ig n n e w s . c o m ] f E b r u A ry 2013 to ground potential, and is largely immune to ground potential disturbances. Ground potential disturbances become a greater concern when multiple low-side current sense resistors are con- figure 1: Application PCb volume comparison. T r e nd waTch : s e ns o r s / mach ine v is io n / a s up p le me nT T o de s ign news T9

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