Even with this fairly conservative design, the ripple reduction is sufficient to enable lower switching frequencies. This is illustrated in Figure 2, which compares the current ripple for different inductor configurations and switching frequencies. The graph demonstrates that a CL operating at 400 kilohertz (kHz) maintains lower ripple than a conventional design at 800 kHz. The reduced switching frequency directly translates to lower switching losses, which include transistor switching losses, dead-time losses in MOSFET body diodes, reverse recovery losses, and gate drive losses. These frequency-dependent losses decrease proportionally as the switching frequency is reduced, resulting in substantial efficiency improvements. Efficiency gains are most visible at light loads, where AC losses are more prominent due to their fixed nature regardless of output current. However, the benefits extend across the entire load range. Figure 3 shows experimental results comparing an 8-phase system with coupled inductors at 400 kHz against a conventional design at 600 kHz, demonstrating approximately 1% improvement at peak efficiency and 0.5% improvement at full load.
Figure 3: Shown is a measured efficiency comparison of the 8-phase DL = 100 nH (dashed curves) and 2 × CL = 4 × 100 nH (solid curves) designs with a common footprint. (Image source: Analog Devices, Inc.)
Improving efficiency without sacrificing transient response Notably, these efficiency improvements are achieved without compromising transient performance. Figure 4 illustrates
current slew rate and C O results in comparable transient responses. While the lower switching frequency of the CL might typically reduce feedback bandwidth, two factors counteract this limitation: the inherent advantages of the multiphase architecture and the enhanced phase margin provided by the coupled design. This phase margin improvement occurs because all coupled phase currents respond simultaneously when the duty cycle changes in response to a transient event in one phase.
the transient behavior of a 4-phase buck converter,
comparing waveforms from an 8-phase design with discrete inductors (DL = 100 nH at 600 kHz) and a configuration using two CLs, each serving 4 phases (2 × CL = 4 × 100 nH at 400 kHz) with V IN = 12 V, V O = 0.9 V for 135 A load steps. Using the same
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