Massimiliano Belloni

A 4-Output Single-Inductor DC-DC Buck Converter with Self-Boosted Switch Drivers and 1.2A Total Output Current

Minimizing power consumption in multi-processor systems requires the use of multiple supplies with a wide range of regulated voltages and currents. Since one inductor per DC-DC converter is expensive, there is an increasing interest in single-inductor-multiple-output (SIMO) DC-DC converters. Recent research results report a SIMO boost converter and various boost or buck converters with two outputs. This 0.5mum CMOS system is a four- output, single-inductor buck converter with independent regulation of each output.

On the design of single-inductor multiple-output DC-DC buck converters

Design techniques for single inductor multiple output (SIMO) DC-DC buck converters are presented. The suitable control of a multiple feedback loop enables the sharing of a single inductor with many outputs with a good stability and limited cross regulation. The method has been verified with simulations at the behavioural and transistor level to obtain four independent regulated output voltages ranging from 0 V to 1 V below the power supply voltage. The use of a suitable analog processing of errors allows obtaining a power efficiency as high as 86%.

A Micropower Chopper—CDS Operational Amplifier

A low-power spur-free precision amplifier, which uses input chopping and correlated double sampling for demodulation, is presented. This circuit employs an AC coupling between the first and the second stage that removes the first stage offset without causing ripple. The input rail-to-rail circuit, fabricated in a mixed 0.18-0.5 μm CMOS technology, operates with supply ranging from 1.8 V to 5 V. The circuit achieves a simulated 168-dB DC gain with an overall current consumption of 14.4 μA. The measured offset voltage over the available samples results in a distribution with 2-μV standard deviation. The obtained input noise density at low-frequency equal to 37 nV/√Hz gives a 5.5 noise efficiency factor.

A 0.18-µm CMOS, 91%-Efficiency, 2-A Scalable Buck-Boost DC–DC Converter for LED Drivers

This paper presents a buck-boost dc-dc converter for LED drivers capable of delivering an output current ranging from 0.1 to 2 A and a variable output voltage ranging between 2 and 5 V, starting from an input voltage spanning from 2.7 to 5.5 V. The dc-dc converter, realized in a 0.18-μm CMOS technology with 5-V option, occupies an area of 4 mm2 including pads. The circuit features automatic mode switching and dynamic sizing of the power transistors to achieve a peak efficiency of 91%. With a switching frequency of 2.5 MHz, the achieved line regulation is lower than 0.1% V-1 and the output voltage ripple is less than 10 mV. The obtained turn-on and load transient settling time are lower than 40 μs, thus allowing pulsed operation of the LEDs, as well as switching among LEDs of different colors.

A 0.18μm CMOS 91%-efficiency 0.1-to-2A scalable buck-boost DC-DC converter for LED drivers

Several emerging portable applications require high-efficiency LED drivers [1-4]. An LED driver is basically a current source that forces the current required for achieving the desired light emission into the LED. In order to increase the LED driver efficiency, besides controlling the LED current, it is necessary to regulate the voltage applied to the LED itself, to minimize the voltage drop across the driver current source and, hence, the power consumption. Depending on the kind of LED and on the current forced through the LED itself (0.1 to 2A in this design) and, hence, on the desired light emission, the voltage required to drive the LED, while maintaining the voltage headroom across the driver current source to the minimum, varies over a wide range (0 to 5V). Starting from a standard voltage supply in the range 2.7 to 5.5V, a buck-boost DC-DC converter is then required (Fig. 16.4.1). The buck-boost DC-DC converter includes the LED in the control feedback loop and has to provide fast turn-on and load transients (on the order of 20μs), in order to allow pulsed operation of the LED itself.

On the design of single-inductor double-output DC-DC buck, boost and buck-boost converters

Design methodologies for Single-Inductor Dual-Output (SIDO) DC-DC switching converters are presented. The suitable control of a double feedback loop enables the single inductor sharing between two outputs with low output voltages errors and limited load-regulation. The design methods to achieve SIDO converters with a wide input supply voltage range and with an overall driving capability as large as 1.4 A have been verified with simulations at the transistor level. The switching frequency can be 3 MHz or more with a small off-chip inductor.

A micropower chopper-correlated double-sampling amplifier with 2µV standard deviation offset and 37nV/√Hz input noise density

A key limit of the chopper stabilized technique is that the low-frequency noise after being shifted up to the chopping frequency is only partially removed by filtering. The auto-zero method does not suffer this limit, but the aliasing of the broadband input noise spectrum imposes the use of large sampling capacitances that, in turn, increase the bias current. The chopper method is the optimal approach for micro-power applications.

High efficiency DC-DC buck converter with 60/120-MHz switching frequency and 1-A output current

This DC-DC buck converter is able to operate up to 120-MHz switching frequency with peak power efficiency of 87% for 75% duty cycle and 93% at 60 MHz. Key feature of this design is a new control method that replaces the conventional op-amp based scheme. The proposed circuit uses a current-mode control and a voltage-to-pulse converter for the PWM. The circuit, fabricated using a 0.18-µm CMOS technology, reaches a peak load regulation of 20 mV/V and line regulation of 0.5 mV/V at 300 mA. The used 36-nH inductance and 4.7-µF capacitor are suitable for SiP realizations.

A voltage-to-pulse converter for very high frequency DC-DC converters

This work presents a new control circuit that uses a voltage-to-time converter to realize high switching frequency DC-DC converters. The proposed solution is adopted in a 20-MHz DC-DC buck converter. Simulation results demonstrate the effectiveness of the approach showing very fast load and line-regulation transient responses (around 1.5 mus) when using a 250-nH inductor and a 10-muF output capacitor. The simulated peak power efficiency is 90%.

Single-Inductor Multiple-Output Dc-Dc Converters

This chapter deals with the design methodologies to obtain DC-DC converters with multiple outputs and only one inductor. The four possible schemes, buck, boost, and inverting or non-inverting buck-boost, are considered. The key specific problems related to the issue are the inductor current switching scheme, the multiple-loops control, the suitable driving of power switches and, accordingly, the converter power efficiency. All the issues are discussed in details. Moreover, design examples of devices integrated with CMOS technologies and the experimental results are presented.