7.3.12 Constant Switching Frequency and Timing Resistor (RT/CLK Pin)

The switching frequency of the TPS54260 is adjustable over a wide range from approximately 100 kHz to 2500 kHz by placing a resistor on the RT/CLK pin. The RT/CLK pin voltage is typically 0.5 V and must have a resistor-to-ground to set the switching frequency. To determine the timing resistance for a given switching frequency, use Equation 11 or the curves in Figure 39 or Figure 40. To reduce the solution size one would typically set the switching frequency as high as possible, but tradeoffs of the supply efficiency, maximum input voltage and minimum controllable on time should be considered.

The minimum controllable on time is typically 135 ns and limits the maximum operating input voltage.

The maximum switching frequency is also limited by the frequency shift circuit. More discussion on the details of the maximum switching frequency is located below.

Equation 11.

Figure 39. Switching Frequency vs RT/CLK Resistance High-Frequency Range

Figure 40. Switching Frequency vs RT/CLK Resistance Low-Frequency Range