A Fast-Transient Fully-Integrated Digital LDO With Current-Estimation Algorithm Based Coarse Loop
Jin-Woong Jang, Ibrar Ali Wahla, Junsik Choi, Muhammad Abrar Akram, In-Chul Hwang
Abstract
In this brief, a fully-integrated output-capacitor-free (OCF) digital low-dropout regulator (DLDO) is proposed utilizing a current-estimation algorithm (CEA)-based coarse loop controller to achieve fast voltage droop ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${V}_{Droop}$</tex-math></inline-formula> ) recovery with improved line and load regulations. The proposed CEA-based controller quickly determines the target output switch-code by estimating the current-voltage ratio of power <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s, enabling fast <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${V}_{Droop}$</tex-math></inline-formula> recovery during load current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathit{I}_\mathit{LOAD}$</tex-math></inline-formula> ) transients. Complementing the CEA-based coarse loop, the proposed OCF-DLDO incorporates asynchronous and fine loops. The asynchronous loop supplies an instant dynamic current during <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathit{I}_\mathit{LOAD}$</tex-math></inline-formula> transients, rapidly restoring the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathit{V}_\mathit{OUT}$</tex-math></inline-formula> , while the fine loop reduces output voltage ripples and quiescent current during steady-state of the DLDO. The proposed OCF-DLDO was fabricated in a 65-nm CMOS process with an active area of 0.075 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula> . Measurement results demonstrate that the proposed DLDO operates with an input voltage range of 0.6 <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> 1.2 V. For a load current step of 26 mA at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathit{V}_\mathit{DD}$</tex-math></inline-formula> = 0.6 V, the proposed DLDO recovers a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathit{V}_\mathit{Droop}$</tex-math></inline-formula> of 140 mV within 95 ns achieving a figure-of-merit of 3.74 ns with a peak current efficiency of 99.6 <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> .