300 mA LDO Using 0.94 μA <i>I_Q </i> With an Additional Feedback Path for Buffer Turn-off Under Light-Load Conditions

Abstract

This paper proposes a 300 mA low-dropout (LDO) regulator using an I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</sub> of only 0.94 μA, which has the advantage of minimizing power consumption in the standby mode of a battery-based system. The LDO uses a source follower buffer with dynamic biasing to maintain loop stability and load transient response performance. Under light-load conditions, the buffer enters a fully-off state because there is a sub-nA bias current. Therefore, the LDO uses a dual output operational transconductance amplifier (DO-OTA) for operation under light-load conditions. The second output of the DO-OTA for light-load operation in the LDO forms an additional feedback path instead of the fully-off buffer. The second output of the DO-OTA is designed to consume a current lower than the bias current of the buffer while operating. Furthermore, the buffer in the LDO is designed for operation above 5 mA I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> . While the buffer is operating, the dynamic biasing current of the buffer is used as the second output of the DO-OTA. The second output of the DO-OTA has lower output impedance characteristics than its main output, so the LDO can secure loop stability under light-load conditions by lowering the DC gain. As a result, the LDO exhibits load transient response performance up to 300 mA by using a minimal I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</sub> under the no-load condition. The LDO is based on a 180 nm bipolar-CMOS-DMOS (BCDMOS) process and covers an area of approximately 256 ×143 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The measured I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</sub> is 0.94 μA under the no-load condition with a maximum load current of 300 mA.