7.3.9 Constant Switching Frequency and Timing Resistor (RT/CLK) pin)

The switching frequency of the TPS54560B is adjustable over a wide range from 100 kHz to 2500 kHz by placing a resistor between the RT/CLK pin and GND 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 7 or Equation 8 or the curves in Figure 6 and Figure 7. To reduce the solution size one would typically set the switching frequency as high as possible, but tradeoffs of the conversion efficiency, maximum input voltage, and minimum controllable on time should be considered. The minimum controllable on-time is typically 135 ns, which limits the maximum operating frequency in applications with high input-to-output step-down ratios. The maximum switching frequency is also limited by the frequency foldback circuit. A more detailed discussion of the maximum switching frequency is provided in Accurate Current-Limit Operation and Maximum Switching Frequency.

Equation 7.

Equation 8.