Multiphase buck converters are widely used in 12 V applications such as datacenters, artificial intelligence (AI) systems, and communications infrastructure. A common theme across these use cases is the need for improved efficiency without compromising performance or increasing the physical footprint. One promising approach involves coupled inductors (CLs). By using mutual inductance between phases, CLs enable superior current ripple cancellation, resulting in significant efficiency improvements while preserving compatibility with conventional layouts. This article briefly outlines the efficiency and layout challenges facing designers of multiphase buck converters. It then introduces CLs, presents experimental results validating the efficiency improvements, and shows how they are applied in converters from Analog Devices. Conventional multiphase buck converter efficiency challenge In high-performance computing and communications systems, efficiency losses in power delivery can have outsized impacts on system cost, reliability, and thermal management. Designers of
conventional multiphase buck designs often face challenges in this regard, particularly under light-load conditions where switching and AC losses become more pronounced. At the same time, power-stage layout and mechanical constraints limit the options available for improving performance. In many systems, there is little room to increase component size, and changes to the printed circuit board (pc board) layout may not be feasible in the face of common footprint strategies. As a result, there is strong interest in approaches that can deliver higher efficiency without requiring substantial changes to the power architecture. Ideally, such solutions would retain the same footprint, allow the use of existing output capacitance (C O ), and maintain transient performance across a wide range of load conditions. CLs address these demands by enabling ripple reduction and switching loss improvements, all within the same physical footprint as conventional designs. How CLs improve power conversion CLs offer an effective way to improve efficiency in multiphase buck converters without altering the layout. Unlike conventional designs that treat each phase
as electrically independent, CLs share a standard magnetic structure that enables interaction between phases. Two key parameters govern this interaction: leakage inductance (L k ) and mutual inductance (L m ). The leakage inductance behaves like the phase inductance (L) in traditional designs, while the mutual inductance introduces magnetic coupling across phases. As current increases in one phase, it induces a voltage in the others that opposes their current change, resulting in significant ripple current cancellation. Equations 1 and 2 define the expected ripple current for conventional discrete inductor (DL) designs (dIL DL ) and CL designs (dIL CL ). These currents depend on the input and output voltages (V IN , V O ), inductances L, L k , and L m , switching frequency (F S ), and a “figure of merit” (FOM). Equation 1:
Equation 2:
Where: ρ = the coupling coefficient = L m /L D = duty cycle N ph = the number of coupled phases Equation 3 lays out the calculations for the FOM. This equation
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