FET Packaging Technologies Merge for Higher Efficiency

May 19, 2004 2:20 PM
By David Morrison, Editor, PETech

By combining two of its packaging technologies, International Rectifier (IR) has created a control and synchronous MOSFET chipset that improves the efficiency of dc-dc converters, particularly high-current VRMs. The chipset exploits the thermal and electrical advantages of the DirectFET package as well as the electrical benefits afforded by the FETKY technology. A FETKY co-packages a HEXFET power MOSFET with a Schottky diode, which reduces the parasitic inductance between the FET and the parallel-connected Schottky, while also saving board space.

The company calls the DirectFET/FETKY combination a DirectFETKY, and the first device bearing this name is the IRF6691, a 20-V synchronous MOSFET with a co-packaged Schottky. When employed in a multiphase converter design, this device boosts efficiency.

Consider a design example where the converter is switching at 1-MHz per phase with full load. In this case, the company claims an efficiency improvement of 1.1% for the IRF6691 over that achieved by existing 20-V synchronous FETs. This comparison assumes use of the same control FET. In addition, the IRF6691 specifies a typical R_DS(on) of 1.2 mΩ (mOhm) at a V_GS of 10 V and a typical Qrr of 26 nC.

The second chipset member is the IRF6617, a 30-V HEXFET control MOSFET in the DirectFET package. The IRF6617 features a total gate charge (Q_g) of just 11 nC, resulting in an on-resistance times gate charge product of 87 mΩ-nC at a V_GS of 4.5. When applied in a 1-U high, 4-phase VRM design switching at 750 kHz per phase, the IRF6691/IRF6617 pair delivers 84.5% efficiency at 90 A of output. Or, if used in an 8-phase embedded VRD10.2 design switching at 400 kHz per phase, the chipset pair provides 87% efficiency at 150 A of output.

Both devices are available now. In quantities of 10,000, unit pricing is $1.49 each for the IRF6691and $0.87 for the IRF6617.

For more information, visit www.irf.com.

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