The internal oscillator uses a timing capacitor (C15) and a timing resistor (R12) to program the oscillator frequency. The operating frequency can be programmed based the curves in Figure 7-1, where the timing resistor is found once the timing capacitor is selected. It is best for the timing capacitor to have a flat temperature coefficient, typical of most COG or NPO type capacitors. For this converter, 40.2 kΩ and 1000 pF were selected for R12 and C15 to operate at 42.5-kHz switching.