SNVS953G December 2012 – May 2021 LM25018
The on-time for the LM25018 device is determined by the RON resistor, and is inversely proportional to the input voltage (VIN), resulting in a nearly constant frequency as VIN is varied over its range. The on-time equation for the LM25018 is determined in Equation 3.
See Figure 6-5. RON must be selected for a minimum on-time (at maximum VIN) greater than 100 ns, for proper operation. This requirement limits the maximum switching frequency for high VIN.