A Compact Fully-Integrated Extremum-Selector-Based Soft-Start Circuit for Voltage Regulators in Bulk CMOS Technologies

Abstract

A fully-integrated soft-start circuit for voltage regulators is presented in this brief. A soft-start strategy based on an extremum selector and a linearly ramped-up reference is developed to prevent any massive in-rush current through the power device during the start-up phase of the regulator. The strategy is realized by a compact on-chip circuit that requires no external components and has minimal transistor overhead, thereby minimizing the implementation area and the cost of the overall regulator. The linearly ramped-up reference is created through the use of nonlinear MOS capacitors available in a low-cost bulk CMOS technology. The proposed soft-start circuit has been implemented in a 0.35-μm bulk CMOS technology as part of a 50-mA linear regulator. The proposed circuit occupies 0.013 mm 2 on silicon, which corresponds to about 13% of the total area of the linear regulator. The soft-start circuit enables the output voltage of the regulator to be linearly ramped up to the steady state under different load currents and charging currents.

Load adaptive start-up scheme for synchronous boost DC-DC converter

“…References [4,5] present a constant current pre-charge circuit which can diminish the inrush current even at higher input voltage, but the converter may be stuck in the start-up operation when the boost DC-DC converter is heavy loaded and over-shoot may occur when the load is close to zero. The ramp-based solutions presented in References [6,7] take a long time to complete the start-up process. There are also off-chip solutions to start up, such as Reference [8], which has an external pin connecting with an external capacitor to control the soft-start process.…”

Ramp-based soft-start circuit with soft-recovery for DC-DC buck converters

“…Many soft-start methods have been reported in the literature [2][3][4][5]. Unfortunately, soft-recovery techniques have not received much attention.…”

Analysis and design of DC-DC converter

“…The soft start circuit is a conventional way to solve the in-rush current during the start-up period. Various techniques are proposed to realize the soft start function, they are mainly classified into analog topology [53][54][55][56][57][58] and digital topology [59,60]. The main idea is to generate a ramp voltage (V soft ) to substitute the reference voltage (V ref ) at the input of the error amplifier.…”

“…As a result, V c is pulled down to define the slow increase in the inductor current and output voltage. This particular inherent function of the proposed ACCF eliminates the need for a dedicated soft-start circuit in the conventional designs [53][54][55][56][57][58][59][60][61][62].…”

“…3. It is experimentally proven to realize the soft-start function inherently which usually requires an additional start-up circuit in the other works[53][54][55][56][57][58][59][60][61][62].…”