The MC34066/MC33066 are high performance resonant mode controllers designed for off-line and dc-to-dc converter applications that utilize frequency modulated constant on-time or constant off-time control. These integrated circuits feature a variable frequency oscillator with programmable deadtime, precision retriggerable one-shot timer, temperature compensated reference, high gain wide-bandwidth error amplifier with a precision output clamp, steering flip-flop, and dual high current totem pole outputs ideally suited for driving power MOSFETs. Also included are protective features consisting of a high speed fault comparator and latch, programmable soft-start circuitry, input undervoltage lockout with selectable thresholds, and reference undervoltage lockout.