A 92%-efficiency wide-input-voltage-range switched-capacitor DC-DC converter

Abstract

The traditional inductor-based buck converter has been the dominant design for step-down switched-mode voltage regulators for decades. Switched-capacitor (SC) DC-DC converters, on the other hand, have traditionally been used in lowpower (<10mW) and low-conversion-ratio (<4:1) applications where neither regulation nor efficiency is critical. However, a number of SC converter topologies are very effective in their utilization of switches and passive elements, especially in relation to the ever-popular buck converters [1,2,5]. This work encompasses the complete design, fabrication, and test of a CMOS-based switched-capacitor DC-DC converter, addressing the ubiquitous 12 to 1.5V board-mounted point-of-load application. In particular, the circuit developed in this work attains higher efficiency (92% peak, and >80% over a load range of 5mA to 1A) than surveyed competitive buck converters, while requiring less board area and less costly passive components. The topology and controller enable a wide input voltage (V IN ) range of 7.5 to 13.5V with an output voltage (V OUT ) of 1.5V. Control techniques based on feedback and feedforward provide tight regulation (30mV pp ) under worst-case load-step (1A) conditions. This work shows that SC converters can outperform buck converters, and thus the scope of SC converter applications can and should be expanded. The input voltage may range from 7.5 to 13.5V, while the converter outputs a nominal voltage of 1.5V, defined by an on-chip bandgap reference. Capacitors C 1 to C 9 are the power-train capacitors, and they are implemented with off-chip ceramic capacitors. The Dickson converter operates in 2 phases, and achieves voltage conversion through charge transfers among capacitors C 1 to C 9 [4]. Switches S 1 to S 12 are the power switches, and the phase in which they are turned on is indicated by the number in bracket next to the switch label in the figure; the switch is turned off in the other phase. Switches S 13 to S 18 are also power switches, but they may turn on in either clock phase depending on the conversion ratio of the converter. For example, in order to attain a conversion ratio of 7.5 to 1, switches S 13 and S 15 are on while switches S 14 , S 16 , S 17 , and S 18 are off during clock phase 1, and switches S 14 and S 17 are on while switches S 13 , S 15 , S 16 , and S 18 are off during clock phase 2. The timing sequence of switches S 13 to S 18 allows the converter to attain 7 different conversion ratios, ranging from 5 to 1 to 8 to 1 with half integer steps. The integrated circuit implementation, in a 0.18µm triple-well CMOS process, is sub-divided into various voltage domains to allow the usage of low-voltage transistors (blocking a maximum of 4V) to accommodate moderate V IN levels, as high as 13.5V [5]. This converter achieves regulation by adjusting its nominal conversion ratio, and by modulating the switch conductance of switches S 1,4,5 [6]. Switch conductance modulation [3] allows tight regulation for line and load variation whereas changing conversion ratio a...

A Light-Load-Efficient 11/1 Switched-Capacitor DC-DC Converter With 94.7% Efficiency While Delivering 100 mW at 3.3 V

“…Recently, however, their switched-capacitor (SC) counterparts have been evolving in this direction [1,2]. Despite widespread usage of inductive converters for this application, SC converters have a key advantage of 50% duty cycle operation as their VCR is mainly set by the SC topology.…”

“…This is an issue as higher switching frequencies are desirable to allow for smaller inductors. SC topologies generally require a larger number of external components than inductive converters, but still compare favorably in terms of area due to efficient component utilization [1,3]. Among SC DC-DC converters, a 3-phase approach [3] requires fewer flying capacitors for a given VCR than regular 2-phase SC converters [4].…”

“…For an output power P o > 20% of P o,max , the system attains an efficiency above 91%, with a peak of 95.5% for a 70mW load from a 37.42V input. In addition of having fewer capacitors than [1], the VCR is higher than [1] and [2]. Next to the 11/1 SC topology, a Multiple-Input Multiple-Output (MIMO) auxiliary rail generator is proposed as a uniform technique to efficiently generate a number of auxiliary supply rails, necessary to reliably generate power switch driving signals.…”

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“…The LV/HV switch drivers are designed to have low current dissipation and sharp clock edge. Protect circuit is also included in the high voltage charge pump [26]. Fig.…”

Fully Integrated Wide Input Voltage Range Capacitive DC-DC Converters: The Folding Dickson Converter

“…1). To this day, this research has given us high power density designs in bulk CMOS [2], [3], even higher power densities when using exotic capacitor types such as trench capacitors [4], [5] or ferroelectric capacitors [6], designs with very fast load transients [7], [5], extremely low ripple designs [8], highly integrated designs as in [9], [10], and even in the world of discrete SMP supplies, capacitive converters are under the spotlight [11]- [13], since in theory capacitive converters can outperform inductive converters [1], [9]. Some effort has also been done to fully integrate inductive converters [14], [15], but they either require extra process steps to have access to good quality inductors, or Manuscript received November 21, 2014; revised January 16, 2015; accepted February 24, 2015.…”