Dual Phase Buck Controller Drives High Density 1.2V/60A Supply with Sub-Milliohm DCR Sensing

June 11, 2015 // By Mike Shriver, Linear Technology
Designers of low output voltage rails for power supply systems are challenged to achieve greater load currents and higher efficiency in diminishing board space. This article by Mike Shriver describes an IC that enables designer to meet these challenges.

The LTC3774 dual output buck controller eases the burden of high load and efficiency at small board space by interfacing easily with DrMOS devices, providing high efficiency and small size by integrating MOSFET and gate driver in the same package. The LTC3774 can sense current across the inductor’s DCR, with values as low as 0.2mΩ, improving efficiency by eliminating the need for a discrete sense resistor. The LTC3774’s peak current mode architecture provides cycle-by-cycle current limit, inherent cycle-by-cycle current sharing and easy to design type II compensation.

High efficiency converter with a small footprint

Figure 1 shows a dual phase 1.2V/60A LTC3774 converter operating at a switching frequency of 400kHz. The power stage for each phase is the FDMF6820A DrMOS, which comes in a 6mm × 6mm QFN package, and a 0.3µH single winding ferrite inductor with a typical DCR of 0.325mΩ. The resulting full load efficiency is 89.8%, as shown in Figure 2. The core of the converter has a current density of 50A/in2.

Fig. 1. Dual phase, 1.2V/60A LTC3774 converter operating at fSW = 400kHz,
7V ≤ VIN ≤ 14V. For higher resolution click here.

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