How to Accurately Calculate Over-Current in High-Side Current-Sense Amplifiers

Abstract: Recently, an engineer asked for a solution to provide high-side monitoring of a 20A load with an accurate over-current detection threshold of better than 5%. There are no easily accessible off-the-shelf solutions that offer the ability to use a low-value sense resistor with less than 5% accuracy! Why 5%? Would 10% be OK? For a 20A load, a 10% current limit would cause the trip threshold to be 18A minimum or 22A maximum, a much wider margin than would be acceptable. What are the factors involved that make 5% so difficult? In this application note, we will discuss the challenges of achieving 5% accuracy, and present a solution that delivers the required accuracy for a high-side current-sense amplifier over-current protection scheme.