Low voltage current limit circuit with temperature insensitive foldback

Abstract

A voltage regulator with a current limit circuit for limiting pass current in a pass transistor below a current limit threshold and a foldback circuit for lowering the current limit threshold when the voltage differential between the input and output terminals of the voltage regulator exceeds a foldback threshold, where the current limit threshold has a negative temperature coefficient, the current limit circuit comprising two transistors coupled to a sense resistor such that the difference in emitter-to-base voltages of the transistors is equal to the voltage drop of the sense resistor, where the collectors of the two transistors provides first and second currents to first and second resistors, respectively, where the first current is responsive to a pass current flowing through the sense resistor and decreases when the pass current increases, where the second current is independent of the pass current, and the foldback circuit provides a third current to the second resistor when the voltage differential between the input and output terminals of the voltage regulator exceeds the foldback threshold. A comparator circuit compares a first voltage drop developed across the first resistor with a second voltage drop developed across the second resistor, and limits base current to the pass transistor based upon the ratio of first and second voltage drops to thereby prevent the pass current from exceeding the current limit threshold.