Many DC-DC converters make use of the “buck” or the “multiphase buck” topology. These topologies are illustrated in FIG. 1. In a single or multiphase buck converter 102, a switching device 104 periodically couples a driven end of an inductor 106 to an input power supply 108. This coupling causes a current to build up through inductor 106 between a converter output 110 and the power supply 108. When the switching device 104 opens, inductor current continues to flow for a time, typically through either or both of a diode 112 and a second switching device 114, and thence into the load. Accordingly, inductor 106 may be referred to as an energy storage inductor, and diode 112 and second switching device 114 couple energy stored in inductor 106 to a load 118. A bypass or filtering capacitor 116 is typically provided to reduce ripple by smoothing voltage provided to load 118. A variable-resistor symbol is used to represent load 118 because effective load resistance may change during operation. Voltage provided to the load 118 is typically sensed by a controller 119 that provides for control and drive of the switching devices 104 and 114; for simplicity of illustration connections between controller 119 and switching devices are not shown. The switching devices are selected by a designer from transistors deemed to be good for switching regulators such as MOS (including CMOS & LDMOS), Gallium Arsenide and Bipolar transistors, and such other electronic switching devices such as gate-turnoff thyristors as known in the art of electronics.
In order to provide for high current capability and reduce ripple, one or more additional phases may be provided to extend the design into a multiphase converter design; where each phase adds an additional switching device, such as switching device 120, diode 121 and/or second switching device 122, and inductor 124 to the design. These switching devices 120, 122 also operate under control of controller 119, and are typically timed to reduce ripple such that device 120 and device 104 do not turn on simultaneously, although they both may be on simultaneously, the timing relationship between turn-on of devices 120, 104 within a converter cycle is a phasing, or a phase relationship between the primary and additional phases of the multiphase converter.
Multiphase DC-DC converters may be designed without magnetic coupling between the inductors 106 and 124 of different phases, or may be designed with specific coupling between the inductors of different phases as described in U.S. Pat. No. 6,362,986 to Schultz, et al., the disclosure of which is incorporated herein by reference.
Multiphase DC-DC converters can be utilized in many applications including digital and analog IC chips. One challenging example is for a power supply to high performance microprocessors. Modern processor integrated circuits often require very low operating voltages, such as voltages at predetermined levels from around one to two and a half volts, and may require very high currents of as much as hundreds of amperes. Further, these processors are often designed with power-saving circuitry that can save considerable power by disabling functional units when those units are not needed, but can cause current demand to soar dramatically over very short periods of time as functional units within the processor are enabled when needed. For example, current demand by some processors may jump by at least 100 amperes within a microsecond, effective load 118 resistance changing sharply between values in the ranges of ohms or tenths of ohms and values on the order of less than a hundredth of an ohm. These processors therefore impose stringent requirements on their associated power supply systems. Typically, these processors are powered from five or twelve volt power supplies thus requiring step-down DC-DC converters such as multiphase buck converters, and large filtering capacitors 116 are provided to allow for load current changes.
Many DC-DC converter applications require a voltage step-up rather than the step-down provided by the buck converter of FIG. 1. Many other architectures for single and multiple-phase converters exist that can meet such requirements.
Among those DC-DC converter architectures that are capable of providing a voltage step up, the most common is the boost converter, single-phase boost converters have been used for many years in such applications as powering the cathode-ray tube of television receivers. FIG. 2 illustrates a multiphase boost converter, having an inductor 202, 204 associated with each phase. Each phase also has at least one switching device, represented by switch 206, and a diode 208. A second switching device, represented as switch 210, may be provided to bypass forward voltage drop of the diode 208; diode 208 and switch 210 together couple energy from inductor 204 to load filter capacitor 212 following each turnoff of switch 206. A controller 214, which may operate under feedback control by sensing load voltage, is provided for driving switching devices 206, 210.