Littelfuse, Inc. v. Mersen USA Newburyport-MA, LLC (17-cv-12375).

  • December 5, 2017

Near the end of 2017, Littelfuse sued Mersen, alleging infringement of U.S. Patent No. 9,564,281 by sale of Mersen’s HP15G family of photovoltaic fuses.  The patent claims fuses having a crimpable terminal for providing a secure connection between a conductor and the fuse.  Mersen filed a counterclaim for declaratory judgment that the accused fuses do not infringe.  Littelfuse answered that counterclaim in 2018. 

The case proceeded through Markman, with a claim construction order issuing on March 6, 2020, and a trial was scheduled to begin on May 11, 2020.  Of course, shortly after the claim construction order was made, the COVID crisis struck, and the trial was indefinitely stayed.  Meanwhile, Littelfuse sought clarification of the Court’s Markman Order, which was denied, and the parties stipulated to noninfringement under that claim construction.  Judgment was entered in May 2021.

Littelfuse appealed the Markman ruling, and in April 2022, the Federal Circuit reversed and remanded.  The asserted claims recited a fuse end cap comprising a mounting cuff, a terminal, and a fastening stem.  Judge Talwani had construed the term “fastening stem” to mean a “stem that attaches or joins other components,” and found that the term “a fastening stem that extends from the mounting cuff and into the second cavity of the termina that receives the conductor” required the fuse to be a multi-piece apparatus, and excluded embodiments wherein either the mounting cuff and terminal or the mounting cuff, terminal and fastening stem were unitary. 

The Federal Circuit noted that the patent had dependent claims that called out the mounting cuff and terminal or the combination of all three elements being formed “from a single, contiguous piece of conductive material” – i.e., unitary.  Given the presumption that an independent claim must cover at least the same scope as a claim that depends from it, this would require the independent claims to also cover unitary end caps.  Further, under the District Court’s construction, the dependent claims would have no scope at all, also disfavored.  The Court further found that the specification supported such a construction, at least insofar as it did not specifically exclude such. 

On remand, Mersen filed an amended answer and counterclaim for declaratory judgment of noninfringement, including noninfringement by a new “Single Piece Design.”  Littelfuse moved to dismiss the counterclaim with respect to the new design for lack of subject matter jurisdiction.  Littelfuse asserted that Mersen’s design, standing alone, could not infringe, and that while Mersen had ordered fuses based on the design from a third-party manufacturer did not create a concrete controversy sufficient to warrant subject matter jurisdiction.  Judge Talwani disagreed, finding that these acts constituted meaningful preparation for selling the new fuse design.  This distinguished cases finding no jurisdiction because in those cases, the accused products were far from complete and were susceptible to design changes.  Further, Mersen had provided the design to Littelfuse, who refused to confirm that the design was non-infringing at a time while the instant suit was pending.  Taken together, this created a reasonable apprehension of suit and an active and substantial controversy supporting jurisdiction.  

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