The MC34129/MC33129 are high performance current mode switching regulators specifically designed for use in low power digital telephone applications. These integrated circuits feature a unique internal fault timer that provides automatic restart for overload recovery. For enhanced system efficiency, a start/run comparator is included to implement bootstrapped operation of VCC. Other functions contained are a temperature compensated reference, reference amplifier, fully accessible error amplifier, sawtooth oscillator with sync input, pulse width modulator comparator, and a high current totem pole driver ideally suited for driving a power MOSFET. Also included are protective features consisting of softstart, undervoltage lockout, cyclebycycle current limiting, adjustable deadtime, and a latch for single pulse metering. Although these devices are primarily intended for use in digital telephone systems, they can be used cost effectively in many other applications. Current Mode Operation to 300 kHz