A soft start circuit for a DC-DC converter has an input reference voltage coupled
to an error amplifier and to a soft start capacitor. A feedback resistor is coupled
between an output node and the error amplifier, whose output is coupled to a pulse
width modulator (PWM). The PWM output is coupled through an inductor to the output
node, to which an output capacitor referenced to ground is coupled. Means is provided
to charge up the soft start capacitor to the output voltage while the converter
is disabled. As a result, when enabled, the converter will not discharge the output
capacitor, but will ramp the output voltage to the voltage Vref without excessive currents.