Method and apparatus for limiting inrush current during startup of a buck converter

A buck converter, comprising:

• a power stage operable to deliver current to an output capacitance coupled to the buck converter;
• and
• a controller operable to control switching of the power stage, including during a startup period in which the buck converter is first enabled, so as to regulate an output voltage of the buck converter,
• wherein during the startup period, the controller is operable to regulate the output voltage to a reference voltage under current-mode control during a first part of the startup period and regulate the output voltage to the reference voltage under voltage-mode control during a second, later part of the startup period,
• wherein the controller is further operable to ramp up the reference voltage from an initial voltage at a beginning of the startup period to a target voltage at an end of the startup period.

A buck converter, comprising:

• a first control loop operable to regulate a first output voltage of the buck converter;
• and
• a second control loop operable to regulate a second output voltage of the buck converter independent of the first control loop,
• wherein the second control loop is operable to use the first output voltage as a reference voltage during a startup period in which the buck converter is first enabled,
• wherein during the startup period, the second control loop is operable to regulate the second output voltage to the reference voltage under current-mode control during a first part of the startup period and regulate the second output voltage to the reference voltage under voltage-mode control during a second, later part of the startup period,
• wherein the first control loop is further operable to ramp the first output voltage from an initial voltage at a beginning of the startup period to a target voltage at an end of the startup period.