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CC (Vcore) and Vdroop Explained
Load line droop (or Vdroop) is an inherent part of any Intel power delivery design. A current proportional to the average current of all active channels flows from through load line regulation resistor RFB. The resulting voltage drop across RFB is proportional to the output current, effectively creating an output voltage droop with a steady-state value. Equation 2 dictates the value for RFB that should be choosen to satisfy the Intel VRD specification (the source of RLL) based on a) the number of power delivery phases (N) and b) the equivalent series resistance (ESR) of the inductor used, effectively known as DCR.
The first question that may come to mind is why droop voltage at all. Truthfully, in most cases the designer may determine that a more cost-effective solution can be achieved by adding droop. Droop can help to reduce the output-voltage spike that results from fast load/current demand changes. The magnitude of the spike is proportional to the magnitude of the load swing and the ESR/ESL of the output capacitor(s) selected. By positioning the no-load voltage (VNL) level near the upper specification limit (bound by the Vccmin load line), a larger negative spike can be sustained without crossing the lower limit. By adding a well controlled output impedance (RLL), the output voltage under load can be effectively 'level shifted' down so that a larger positive spike can be sustained without crossing the upper specification limit (such as when the system suddenly leaves a heavy load condition). This makes sense as the heavier the CPU loading the smaller the potential negative spike and vice versa for lower CPU loading/positive spikes. The resulting system is one in which the system operation point is bound by Vccmin and Vccmax at all times (although short excursions above Vccmax are allowed by design).