Switching voltage regulators are commonly used for both step-up and step-down applications, and differ from linear regulators by means of pulse-width modulation (PWM) implementation. Switching regulators control the output voltage by using a current switch (internal or external to the IC regulator) with a constant frequency and variable duty-cycle. Switching frequencies are generally from a few kHz to a few hundred kHz. The switch duty-cycle ratio determines how much and how quickly the output supply voltage increases or decreases, depending on the load state and input source voltage. Some switching regulators utilize both variable switching frequency and duty-cycle, but these are not commonly used for FPGA/CPLD applications.
The clear advantage of switching regulators is efficiency, as minimal power is dissipated in the power path (FET switches) when the output supply voltage is sufficient for the load state. Essentially, the power converter "shuts off" when power is not needed, due to minimal switch duty-cycle. The disadvantage of switching regulators is complexity, as several external passive components are required on board. In the case of high-current applications, external FET ICs are required as the IC-converter acts only as control logic for the external FET switch. Output voltage ripple is another disadvantage, which is generally handled with bypass capacitance near the supply and at the load.