This presentation will consider three control topologies commonly used in buck regulator design: voltage mode, current mode, and constant on-time. In voltage mode control, the output voltage is used as the feedback control element. The switching frequency remains constant for a voltage mode controller. A current mode controller adds current control into the loop. The control can come from either the peak of the inductor current or the average of the inductor current. As with voltage mode, the frequency is fixed. Constant on-time regulators use the voltage ripple as calculated previously for control. The on-time pulse starts when the valley of the ripple voltage hits the reference voltage. The tON time is fixed, while tOFF varies based off the inductor, input voltage and output voltage. The constant on-time regulator is not a fixed frequency device, but it is a pseudo-fixed frequency. With a given VIN and VOUT, the frequency will remain constant, but when a disturbance occurs, the frequency will change until the disturbance ends.