While it may be tempting to use the resistance of a known area of PCB trace or copper area as a sense resistor, TI does not recommend this for precision measurements.

The tempco of copper is typically 3300 to 4000 ppm/°K (0.33% to 0.4% per °C), which can vary with PCB processes.

A typical surface mount sense resistor temperature coefficient (tempco) is in the 50 ppm to 500 ppm per °C range offering more measurement consistency and accuracy over the copper trace. Special low tempco resistors are available in a range from 0.1 ppm to 50 ppm, but at a much higher cost.