Making Sense of Two-Wire Current-Sense Resistors

Focus:

Four-wire sense resistors provide two power connections and two sense wires in order to make a precision measurement. Newer two-wire devices are available in values as low as 250 micro-ohms (µΩ), with wide pads to minimize inductance. Although we could assume that such devices could be represented as a single resistor with two connections, this assumption could lead to incorrect measurements in an actual application where the effects of PCB interconnects come into play. In this article, the author uses simple but precise test set ups to perform measurements on a metal-foil current-sense resistor mounted to a small PCB. The author uses these measurements to develop a finite element analysis model of the resistor+PCB combination, which is then used to obtain some insights into the effect of the PCB characteristics (copper weight, use of traces versus planes, positioning of terminations) on the resistor value seen in the application.

What you’ll learn:

• How to model a two-wire sense resistor in an application
• How to evaluate the effects of PCB layout on the value of a two-wire sense resistor

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Author & Publication:

Steven Sandler, Picotest, Phoenix, Ariz., How2Power Today, Jul 30 2012

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