The first step of this design procedure is to determine the switching frequency of the regulator. Consider the trade-offs of a higher switching frequency versus a lower switching frequency. A higher switching frequency allows for the use of a lower-valued inductor and smaller output capacitors, which leads to the smallest solution size. A lower switching frequency results in a larger solution size, but better efficiency. In general, the selected switching frequency allows for the minimum tolerable efficiency to avoid excessively large external components.

A switching frequency of 600 kHz is a good trade-off between efficiency and solution size. The appropriate resistor value is selected based on the resistance versus frequency graph (see Figure 6-5) or calculated using Equation 1. The value of R4 is calculated to be 78.4 kΩ and the nearest standard value resistor of 78.7 kΩ is selected. A resistor must be placed from the FREQ pin to ground, even if an external oscillation is applied for synchronization.