8.2.2.2 Step One: Select the Switching Frequency

The first step is to decide on a switching frequency for the regulator. Typically, it is desirable to choose the highest switching frequency possible since this produces the smallest component solution size. The high switching frequency allows for lower value inductors and smaller output capacitors compared to a power supply that switches at a lower frequency. However, the higher switching frequency causes extra switching losses, which degrade the performance of the converter. This SWIFT™ converter is capable of running from 200 kHz to
2 MHz. Unless a small solution size is the top priority, a moderate switching frequency of 500 kHz is selected to achieve both a small solution size and high-efficiency operation. Using Equation 13, R_T is calculated to be
81.34 kΩ. A standard 1% 82.5-kΩ value was chosen for the design.

Equation 13.

where

• R_T is in kΩ
• F_SW is in kHz