Switching controller chip with internal but not external soft start

Abstract

A DC-to-DC converter which includes a switching controller or regulator (implemented as an integrated circuit) and circuitry external to the controller or regulator chip, where the controller or regulator chip includes soft start circuitry but requires no component external thereto (other than the external circuitry present in DC-to-DC converters having no soft start capability) in order to accomplish a soft start. The invention is especially useful where it is impractical or undesirable to implement the controller or regulator chip with a pin dedicated for connection to an external soft start capacitor or other component or circuit for performing a soft start operation. Other aspects of the invention are a controller or regulator chip for use in such a converter, and a method for performing DC-to-DC conversion using such a switching controller or regulator chip and external circuitry coupled to the controller or regulator chip to generate an output potential which increases to a regulated value during a soft start period and remains at the regulated value during steady state operation. Preferably, the controller or regulator chip includes an on-board capacitor, charging circuitry for charging the capacitor during a soft start period, an overvoltage comparator which compares the voltage across the capacitor with a feedback potential (proportional to the output potential of a DC-to-DC converter with which the controller or regulator chip is used), and an OR gate having a first input coupled to receive the output of the comparator and a second input coupled to receive a reset signal which (during steady state operation of the controller or regulator chip) triggers the switching off of the converter's power transistor.