TPS54625 uses an adaptive on-time control scheme and does not have a dedicated on board oscillator. The TPS54625 runs with a pseudo-constant frequency of 650 kHz by using the input voltage and output voltage to set the on-time one-shot timer. The on-time is inversely proportional to the input voltage and proportional to the output voltage. The actual frequency may vary from 650kHz depending on the off time, which is ended when the feed back portion of the output voltage falls to the V_FB threshold voltage.