ICs for measuring currents usually employ external sense resistors with values of a few tens of milliohms. Not only are such resistors difficult to obtain, the circuit board layout can have a disturbing effect on the accuracy of the measurement. This problem is eliminated by the LM3822 and LM3824 ICs from National Semiconductor (www.national.com), which have built-in sense resistors with a value of only 3 mW. A delta-sigma modulator converts the measured value into a digital value.
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