4 Suggestions and Conclusion

There are several advantages to using copper traces in place of a normal shunt resistor. One advantage is the reduced cost of implementation. Another is the fact that they can handle large currents, depending on the size of the trace. This must be balanced against the fact that copper trace thickness is highly susceptible to variations in the PCB manufacturing process, and that temperature variation due to ambient conditions and current running through the trace can affect the resistance measurements.

Copper trace shunt resistors are not suitable for any application that requires a high degree of accuracy. The only way to assure that the trace resistance is reasonably close to what is expected is to use a very large continuous trace with no gaps. This is also the only trace that can be used to handle large currents.

Alternatively, for applications where cost is more important to optimize than accuracy, it is possible to use a two-point calibration method to account for manufacturing errors, but it is crucial to realize that the approximation afforded by the calibration becomes significantly worse as more boards are made, as PCB manufacturers are unable to completely control how much copper is plated on the board. The calibration prediction also gets worse for larger currents, as these currents heat the trace more and cause more deviation from the expected values.

Some factors proved to not be as important to implementing a copper trace shunt. No significant difference in measurement was noticed between tap off points, either at the bottom or the center. Also, trace shape appeared to not have much of an impact on the overall resistance of the trace, but this is difficult to prove conclusively.

Copper traces, while an inexpensive alternative to SMT shunt resistors, must be used with caution to measure current. A solution using this method can not be assured to behave as expected, and requires adjusting calibration constants to account for variability.