This slide shows the basic waveforms associated with a buck regulator. DH is the control signal to the high-side FET. As the controller turns on the high-side FET, current ramps up in the switch. At the same time, current also ramps up in the inductor and the voltage of the phase node hits VIN. When the high-side switch is turned off, current ramps down in both the inductor and the low-side FET and the voltage at the phase node is pulled to ground. The signal at VPHASE is then filtered to form VOUT. The amount of time the high-side FET is on is defined as tON. The amount of time the high-side FET is off is defined as tOFF. The time of tON plus tOFF is defined as T, or total cycle time.