DC-DC CONVERTER SOFT START CIRCUIT USING DUTY CYCLE LIMITING

摘要

A DC-DC converter (104, 110, 106, 108) is provided in which a pulse width modulator (150) connected to a transistor (110) switches the transistor on and off to permit a capacitor (108) to charge or discharge. A maximum duty cycle of the transistor is increased by the pulse width modulator once the capacitor has reached a predetermined voltage. The maximum duty cycle is set by a system clock delay. The pulse width modulator contains latches (114, 116, 118, 120) whose inputs, outputs and resets are connected together to select the desired maximum duty cycle through a multiplexer, logic that combines the selected duty cycle with a regulator feedback pulse to determine an actual duty cycle, a timer (122) that selects the maximum duty cycle if the capacitor has not reached a predetermined voltage within a predetermined amount of time (130), and logic that enables operation of the pulse width modulator using an externally provided enable signal.