Soft start circuit and method for dc-dc voltage regulator

A voltage regulator comprising:

• PNP pass transistor that includes an emitter coupled to receive an input voltage and a collector coupled to provide a regulated voltage and a base;
• an amplifier circuit coupled to produce a control voltage on a control line that is coupled to control a voltage at the pass transistor base, based at least in part upon a difference between reference voltage and the regulated voltage;
• a switch that includes a first transistor configured to transition, between a first switch state in which the first transistor operatively couples the control line to a turn-off voltage having a value to turn off the pass transistor and a second switch state in which the first transistor decouples the control line from the turn-off voltage;
• a switch control circuit that includes a second transistor and a delay circuit, wherein the second transistor turns on in response to a ramp up of the input voltage and wherein the delay circuit is configured to delay providing a turn-off signal to the second transistor until the input voltage ramps up to at least its steady state, wherein the second transistor is configured to turn off the first transistor while the second transistor is turned on and to turn on the first transistor in response to the second transistor turning off.

In a voltage regulator circuit that includes, a pass transistor coupled to receive a supply voltage and to provide a regulated voltage;

• and an amplifier circuit coupled to receive a reference voltage and an indication of the regulated voltage and to provide a control signal on a control line that is coupled to control turn on of the pass transistor, the method comprising:
• receiving a supply voltage ramp up at a supply node of a pass transistor;
• in response to receiving the supply voltage ramp up, coupling the control line to a turn-off voltage that turns off the pass transistor for a time interval that is long enough for the control line to charge to at least a normal steady state value;
• and
• decoupling the turn-off voltage from the control line after the time interval.