PTAB

IPR2020-01350

Monolithic Power Systems Inc v. Volterra Semiconductor LLC

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1. Case Identification

2. Patent Overview

  • Title: Coupled Inductor for DC-to-DC Converters
  • Brief Description: The ’955 patent discloses magnetic circuit designs for coupled inductors used in multi-phase DC-to-DC converters. The invention describes a magnetic core with a passageway for two or more windings wound around a common leg, where the component dimensions can be adjusted to tune magnetizing and leakage inductance, thereby reducing current ripple in the converter.

3. Grounds for Unpatentability

Ground 1: Claims 12-15 are obvious over Kung in view of Faulk.

  • Prior Art Relied Upon: Kung (Application # 2002/0067234) and Faulk (Patent 6,084,499).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner asserted that Kung taught a compact inductive device that met most limitations of independent claim 12. This included a U-I magnetic core, a passageway for windings, an outer leg partially defining the passageway, and single-turn, C-shaped windings with ends extending to the bottom for soldering to a printed circuit board (PCB). Petitioner contended, however, that Kung did not explicitly disclose the winding "separation distance being greater than the height of the passageway." Faulk was alleged to supply this missing element, as it described adjusting the coupling coefficient in a similar U-I core by varying this specific dimensional ratio.
    • Motivation to Combine: Petitioner argued a person of ordinary skill in the art (POSITA) would combine Faulk's teachings with Kung's inductor to achieve a desired coupling coefficient. Both references addressed DC-DC converter applications where component size and performance are critical. A POSITA seeking to control the coupling in Kung’s compact inductor would have looked to analogous art like Faulk, which explicitly taught how to modify core and winding geometry to adjust magnetic coupling.
    • Expectation of Success: The combination was argued to yield predictable results. It involved applying Faulk's established principles of magnetic coupling to the structurally similar inductor disclosed in Kung. Faulk provided a successful example of separating windings to reduce coupling, which Petitioner argued demonstrated the predictability of the proposed modification.

Ground 2: Claims 16, 17, and 19-22 are obvious over Kung in view of Wong.

  • Prior Art Relied Upon: Kung (Application # 2002/0067234) and Wong (a 2001 PhD dissertation on multi-channel interleaving voltage regulators).
  • Core Argument for this Ground:
    • Prior Art Mapping: This ground challenged the system claims directed to a two-phase DC-to-DC converter. Petitioner argued that Kung disclosed the physical coupled inductor structure, while Wong disclosed the electrical converter circuit that utilizes such an inductor. Wong taught a two-phase buck converter circuit with two windings switched 180 degrees out of phase to reduce current ripple and improve transient response. The proposed combination involved integrating Kung's physical inductor into Wong's electrical circuit schematic to realize the claimed converter.
    • Motivation to Combine: A POSITA would be motivated to use Kung's compact, versatile, and easily manufacturable inductor as the coupled inductor component within Wong's converter design. Petitioner asserted this would be a simple and logical substitution of one known component for another to gain the benefits of both arts—namely, the efficient circuit design of Wong with the advantageous physical properties of Kung's inductor. Kung's disclosure was said to expressly teach its versatility for use in various circuits.
    • Expectation of Success: Petitioner claimed a high likelihood of success, as the integration was a predictable combination of a known mechanical/magnetic component (Kung's inductor) with a known electrical circuit (Wong's converter) for their respective intended purposes.

Ground 3: Claims 16-22 are obvious over Wong in view of Faulk.

  • Prior Art Relied Upon: Wong (a 2001 PhD dissertation) and Faulk (Patent 6,084,499).

  • Core Argument for this Ground:

    • Prior Art Mapping: Petitioner argued that Wong disclosed a complete two-phase DC-to-DC converter circuit using a coupled inductor with an E-I core structure that featured a gapped center leg. Faulk, in turn, taught an alternative U-I core with an open space between the windings, which it presented as a superior design for simplifying assembly and reducing component size compared to gapped-leg designs. The proposed combination involved replacing Wong's gapped E-I core with Faulk's simpler and more efficient open-space U-I core structure.
    • Motivation to Combine: A POSITA would be motivated to modify Wong's inductor based on Faulk's explicit teaching that its open-space configuration is an improvement over gapped center-leg designs for parallel-driven windings, the exact configuration used in Wong. This modification would directly advance the shared goal of both references to create smaller, more efficient, and more manufacturable DC-to-DC converters.
    • Expectation of Success: Petitioner asserted a high expectation of success because the combination was based on substituting one known magnetic core structure for another, improved structure within the same technical field. The underlying magnetic and electrical principles of the converters in Wong and Faulk were argued to be identical, making the outcome of the substitution highly predictable.

  • Additional Grounds: Petitioner asserted additional obviousness challenges, including that claims 12-15 are obvious over Faulk in view of Kung, and claim 18 is obvious over Kung in view of Wong and Faulk.

4. Relief Requested

  • Petitioner requested the institution of an inter partes review and the cancellation of claims 12-22 of Patent 7,772,955 as unpatentable under 35 U.S.C. §103.