MHz Buck Converter Research Articles

Optimum Phase Count in a 5.4-W Multiphase Buck Converter Based on Output Filter Component Energies

This article presents an analysis of low-power, multiphase interleaved buck converters to illustrate the extent to which adding more phases is beneficial for reducing the passive components’ sizes. The analysis focuses on a typical converter application with a wide operating duty cycle range and requires good load transient. It is shown that by restricting the phase current ripple, the theoretical reduction in total inductor peak energy predicted for increased phase numbers is limited. The article assesses the benefit of inductor coupling and presents guidelines for coupling factor selection to avoid steady-state inductance roll-off over the wide input voltage range. Standard printed circuit board (PCB) manufacturing design rules are shown to place a practical phase count limit considering the reduction in total inductor size. PCB integrated, air-core solenoid and spiral inductors are implemented in both single- and two-phase 5.4 W, 20 MHz buck converter prototypes. When compared with single-phase designs, two-phase spiral inductors are 44% smaller, and the two-phase solenoid has a 54% lower loss. The two-phase prototype converter achieves better overall efficiency and peaks at almost 90% at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_IN</i> = 4.5 V, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_OUT</i> = 1.8 V, and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F_SW</i> = 20 MHz.

Analysis and Design of the Output Filter for Buck Envelope Amplifiers

The efficiency of linear power amplifiers can be improved by modulating its supply voltage according to the peak value of the signal that is being amplified in a technique usually known as envelope tracking. High bandwidth dc/dc converters called envelope amplifiers (EAs) are used to carry out the supply modulation in an efficient manner. In the case of linear RF power amplifiers, the bandwidth requirements over the EA strongly depend on the signal being amplified: in modern telecommunication applications it can range from several hundred kilohhertzs to a few tens of megahertz. The path to achieve such bandwidths usually goes through increased switching frequencies and/or reduced ratio of switching frequency to converter bandwidth. However, these may lead to lower converter efficiency and increased distortion, making the design of EAs a challenging task. This paper addresses the analysis and design of the output filter for Buck converters operating as EA. The output filter must provide enough attenuation at the switching frequency and harmonics to guarantee a desired level of distortion while enabling tracking of wide-bandwidth envelope signals with high converter efficiency. This paper focuses on the use of high-order filters (up to sixth-order Bessel-Thomson, Butterworth, and Legendre-Papoulis filters) in a buck dc/dc converter working as an EA. The filters are analytically described and characterized, and a design procedure that takes into account the major design constraints is proposed, allowing the selection of the appropriate filter for a given application. The proposed analysis and design method are supported by simulation results, as well as by experiments obtained using a 1 MHz buck converter operating as an EA.

Advanced Control for Very Fast DC-DC Converters Based on Hysteresis of the ${C}_{out}$ Current

The bandwidth achievable by using voltage mode control or current mode control in switch-mode power supply is limited by the switching frequency. Fast transient response requires high switching frequency, although lower switching frequencies could be more suitable for higher efficiency. This paper proposes the use of hysteretic control of the output capacitor ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Cout</i> ) current to improve the dynamic response of the buck converter. An external voltage loop is required to accurately regulate the output voltage. The design of the hysteretic loop and the voltage loop are presented. Besides, it is presented a non-invasive current sensor that allows measuring the current in the capacitor. This strategy has been applied for DVS (dynamic voltage scaling) on a 5 MHz buck converter. Experimental results validate the proposed control technique and show fast transient response from 1.5 V to 2.5 V in 2 μs.