The CS5307 is made on a new high-speed bipolar process, on which 6- and 3-phase versions will be built. Higher integration also is on the drawing board with the next generation of multiphase controllers, including on-chip gate drivers and MOSFETs. Presently, ON Semiconductor offers 2-phase chips with integrated drivers.
While most companies have expanded into the notebook arena with multiphase solutions, Linear Technology set its sights on mobile applications from the start. It has developed a current-mode polyphase scheme that forms the basis of its biphase designs. For applications that need more than two phases, the polyphase controllers can be easily cascaded to achieve up to 12 phases.
"By operating at higher frequencies per phase and integrating the MOSFET drivers with the controller, the polyphase solution offers the smallest circuit profile and footprint, and reduced capacitance on both the input and output," says Tony Armstrong, Linear Tech's product marketing manager. "To improve thermal management, it offers accurate current sharing on each phase and faster transient response."
Linear Technology continues to refine its products by doubling the frequency/phase and tightening tolerances over predecessor products without compromising conversion ef- ficiency and load step response. For instance, one of the latest members, the LTC3728, offers 550 kHz/phase.
The rising demands of upcoming notebook processors and tighter IMVP III and IV specifications will soon force Linear Technology to go to 3-phase versions. It will release several parts in this range by month's end, starting with the LTC3732. This 3-phase synchronous step-down controller drives all N-channel external power MOSFETs in a phase-lockable fixed-frequency architecture, offering up to 600 kHz per phase. A unique feature is the choice of output stage shedding or Burst mode, to optimize light load efficiency.
More Companies Join In: International Rectifier, Microsemi, National Semiconductor, Maxim Integrated Products, and Texas Instruments all plan to introduce multiphase voltage controllers. Eying mobile systems, National Semiconductor is preparing both 4- and 2-phase hysteretic controllers.
"Current sharing or current balancing is a critical performance consideration," says Maria Laughlin, marketing manager for National's power-management ICs. "This is critical at the maximum current load for the system designer who wants to use optimal ratings for inductors, current-sense resistors, and FETs. Balanced current sharing avoids having to use larger components, which impact the total-solution size and cost."
Newcomer Microsemi, though, has developed a proprietary load-sharing scheme to accomplish accurate forced and programmable current sharing. In this patent-pending scheme, voltages on the primary side of each phase are matched to attain an accuracy of better than 10%. Its multiphase controller can realize dc-dc converters that conform to IMVP IV specs.
Intersil and Primarion are jointly developing controllers to meet the demands of advanced microprocessors, which will approach 10-GHz clock speeds in a few years. "Together, we will enable a new class of multigigahertz power-management solutions with digital control to provide new ways of delivering power to future processors," says Steve Rivet, Intersil's vice president of marketing.
The first fruit of this joint effort, a digitally programmable controller, can furnish up to eight phases per chip. Available from both Intersil and Primarion, it will target VRM 9.X specifications, with VRM 10.0 to follow.
While others ready digital control to multiphase solutions, Volterra Semiconductor has taken the lead. Implementing its proprietary digital technique, it has developed multiphase regulators for both VR-Down and VRM specifications.