LDO with improved stability

摘要

A low drop-out (LDO) voltage regulator which parallels a second pass device to a first pass device, where the second pass device has in series a small resistor. The small value resistor is a substitute for bond wires or capacitors with very low equivalent series resistances (ESR). A fast feedback loop is coupled to the junction of the second pass device and the small resistor and provides, via a Miller capacitor, a feedback signal to the amplifier of the voltage regulator. The added second pass device returns circuit stability by moving the fast-loop high frequency zero node back within the bandwidth of the circuit.

主权项

1. A modified low drop-out voltage regulator, comprising:
an amplifier stage comprising: an amplifier having an input and an output; where the input is the output of a low drop-out voltage regulator output node; a buffer having an input and an output, its input coupled to said output of said amplifier, to buffer the output signal of said amplifier, said buffer providing an output signal; a first pass device of an output stage in communication with said buffer output to provide a first current at a first output node of said output stage; a second pass device of said output stage in communication with said buffer output to provide a second current at a second output node of said output stage; a bond wire coupled at one end to said first output node and at its other end to said low drop-out voltage regulator output node; a resistive means, in series with said bond wire, coupled between said second output node and said low drop-out voltage regulator output node; a main feedback loop to regulate an output voltage Vout at said low drop-out voltage regulator output node, where one end is coupled to the junction of said bond wire and said low drop-out voltage regulator output node and the other end is in communication with said amplifier input; and a fast feedback loop to feed back high-frequency disturbances, where one end of said fast feedback loop is coupled to said second output node and where the other end is coupled to said buffer input node, said fast feedback loop comprising a Miller feedback capacitor.