A High-Efficiency Fast-Transient LDO With Low-Impedance Transient-Current Enhanced Buffer
Xiao Zhao, Qisheng Zhang, Yaping Xin, Shuoyang Li, Lanya Yu
Abstract
This article proposes a new low-impedance transient-current enhanced (LTE) buffer, which is applied for low-dropout regulator (LDO) with large off-chip capacitor. The LTE buffer is based on current-shunt feedback technique and two ac coupling networks, which can achieve an extremely low output impedance and high charging/discharging current of the gate of power transistor at load transient response, while maintaining low-quiescent current consumption under the full-load range. In addition to containing the LTE buffer, the proposed LTE-LDO employs recycling-folded-cascode amplifier as the error amplifier, which has the advantage of high loop gain, loop bandwidth, and current efficiency. Meanwhile, simple Miller compensation with a nulling resistor is employed for frequency compensation and a complete small-signal analysis under different load current conditions is given in this article. This design has been implemented in semiconductor manufacturing international corporation 0.18 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m complementary metal–oxide–semiconductor process and the experimental results show that the quiescent current consumption is about 48 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> A, and the maximum current efficiency of the LTE-LDO is 99.976 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> . The measured transient response shows that under the condition of 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> F load capacitance, when the load current changes to 200 mA/100 ns, the output voltage change is 76 mV.