A fraction of the DC output voltage is compared with an internal reference in the error amplifier, whose output is compared with the output of a current-sense amplifier to drive a one-shot timer that is on for a period of time that depends on the ratio VOUT/VIN. The one-shot timer turns on the upper gating transistor and the current in inductor L1 ramps up. When the one-shot times out, the transistor is turned off, and the current ramps down.  After an interval determined by the minimum-off-timer and the minimum (“valley”) current, the one-shot timer is pulsed again. The on-chip one-shot timer employs input voltage feedforward for maintaining a constant frequency in the steady state.