App note from Richtek on the comparison of current sensing methods using inductor’s DCR. Link here (PDF)
Current sensing plays an important role in DC/DC regulator systems, especially in multi-phase buck converters for CPU VCORE applications. In VCORE applications, the current signals are used to decide the load-line droop, per-phase current balance, current reporting, and over current protection. Moreover, if the control topology is current mode, the current signal will directly affect the system stability. Therefore achieving accurate current signals is very important.
Generally, the inductor DC resistance (DCR) current sensing technique is widely used in CPU voltage regulator (VR) applications due to its lossless characteristic. However, the DCR current sensing method needs to parallel an RC network beside the inductor, and is likely to be near noisy nodes like the phase node or other PWM signals. It offers many opportunities to add noise which may decrease the current sensing accuracy. In addition, the offset and bandwidth of the current sensing op amp can also decrease the sensed current signal accuracy or distort the current signal, and generally present a great challenge to acquiring a clean current signal.