Overcome the Challenges of Using Sub-Milliohm SMD Chip Resistors (Part 1) (Download)
The simplest and most cost-effective way of converting a measured current to a voltage signal is to use a low-ohmic-value current-sense resistor. The upswing in products containing batteries, motors, or actuators that call for current monitoring or control has led to huge market growth for current-sense chip resistors with values below one ohm over the last two decades.
More recently, though, driven by power-efficiency demands and enabled by low-noise voltage-sense amplifiers, the value range has extended downward from milliohms to hundreds of microhms. Such low ohmic values present challenges to the user at many stages in their design and manufacturing processes.
This two-part series considers the nature of these challenges and suggests strategies to overcome them at various stages, including component selection, PCB layout design, verification of the ohmic value of unmounted components, and critical assembly processes. Each stage features potential pitfalls but also opportunities to quantify and minimize error and variation.