Electronic Design

Transformer Technology License Will Spur New Applications

Midcom Inc. of Watertown, S.D., has licensed its ferrite, multilayer, low-temperature cofired ceramic (LTCC) technology to Tamura Corp. of Tokyo, Japan. The agreement provides a second source for the LTCC-based transformers while helping promote their use in new applications.

Packaged as surface-mountable leadless chip carriers, Midcom's LTCC transformers target both signal and power applications, where they offer smaller size, superior reliability, and potentially lower costs than traditional wirewound components (see the figure). In particular, the transformers can replace the small handwound toroids that provide isolation in telecom and datacom applications.

The licensed technology covers innovations described in two Midcom patents. One details techniques for routing screenprinted silver conductors through the ferrite-based ceramic material that serves as the transformer's core. The second documents the design of patterns for a high-reluctance material that manages the transformers' magnetic field, orienting the transformer's magnetic flux lines in the desired direction. The high-reluctance material also increases the coupling coefficient as well as dielectric isolation from primary to secondary.

In addition to these innovations, the technology relies heavily on the ferrite-based ceramic material's composition. Midcom credits its thick-film material supplier, Electro Science Laboratories, King of Prussia, Pa., with helping to develop a ferrite green tape that could be cofired with the required vias and conductors. This tape differs from the tape used to create ceramic multilayer capacitors and LTCC modules for RF and microwave applications.

While others have developed LTCC transformers using ferrite materials, they have been able to achieve coupling coefficients of only 0.75. In contrast, Midcom has obtained a coupling coefficient of 0.97. In terms of power, Midcom's LTCC transformers handle up to 0.75 W. Additionally, primary-to-secondary dielectric isolation is well above the 1500 V ac commonly specified for telecom designs.

The technology may also be applied to develop inductors like those needed in low-voltage buck converters. In dc bias applications, the LTCC inductors offer performance on a par with drum-core inductors, but with a chip inductor profile. Also, shielding is built in as transformer windings are embedded in a ferrite material.

Tamura's license covers xDSL, analog modem, LAN, and switch-mode power-supply isolation applications, which are typically under 10 MHz. Midcom's technology currently achieves a self-resonant frequency of 60-MHz, suiting it for operation as high as 40 MHz. Yet the technology potentially could be extended to nearly 1 GHz, placing the LTCC transformers in competition with wound toroids and binocular-core transformers. Another possibility stems from the ability to fabricate capacitors from the ferrite material. This makes possible the development of ferrite-based LTCC modules.

For information about Midcom, see www.midcom-inc.com and go to the MicroMagnetic page. Or, contact Darryl Schofield at (605) 882-0343 or [email protected]. For details on Tamura, see www.tamuracorp.com, or contact Jim Coleman at (909) 699-1270 or [email protected].

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