Switching voltage regulators are widely used in modern electronic systems for a variety of applications such as computing (server and mobile) and POLs (Point-of-Load Systems) for telecommunications because of their high efficiency and small amount of area/volume consumed by such converters. Widely accepted switching voltage regulator topologies include buck, boost, buck-boost, forward, flyback, half-bridge, full-bridge, and SEPIC topologies. Multi-phase buck converters are particularly well suited for providing high current at low voltages needed by high-performance integrated circuits such as microprocessors, graphics processors, and network processors. Buck converters are implemented with active components such as a pulse width modulation (PWM) controller IC (integrated circuit), driver circuitry, one or more phases including power MOSFETs (metal-oxide-semiconductor field-effect transistors), and passive components such as inductors, transformers or coupled inductors, capacitors, and resistors. Multiple phases (power stages) can be connected in parallel to the load through respective inductors to meet high output current requirements.
Typical multi-phase buck converter designs for CPU core voltage (Vcore) applications utilize from two to six or more phases, where Vcore is the power supply voltage supplied to a CPU (central processing unit), GPU (graphics processing unit), or other device containing a processing core. Conventional multi-phase buck converter designed for Vcore applications use the same inductance value for each phase. Regulators for Vcore applications must support both high load operation when the processor operation activity level and its current consumption are high, and light load operation when the processor operation activity level and its current consumption are low. In addition, regulators often have tough transient specifications to accommodate quickly when switching between light load and high load operation while maintain good regulation, and therefore require relatively low inductance values such as 150 nH per phase. For end customers, it is desirable that the design pass such stringent transient specifications, while also operating with good light and peak load efficiencies. To improve light load efficiency, the phases should have higher inductance values as this reduces the ripple current in the inductor. However, the inductance value is limited to support high phase currents. Generally the saturation current for an inductor decreases as the inductance is increased for the same physical size, so lower inductances can support higher output current. Additionally, phases with higher inductance values are far less likely to pass Vcore fast transient load response specifications, so there is a trade-off required in selecting the optimal inductance for these designs. Besides Vcore applications, multi-phase voltage regulator can be used in memory applications where an asymmetrical phase inductance approach can be implemented with similar positive results.
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