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MOSFET/Schottky device up DC/DC converter efficiency

Posted: 14 Dec 2007 ?? ?Print Version ?Bookmark and Share

Keywords:power MOSFET? Schottky diode? DC/DC conversion?

Vishay Intertechnology Inc. has released a single-chip power MOSFET and Schottky diode device that is said to improve operational efficiency by up to 6 percent in DC/DC conversion applications compared to circuits using any previous monolithic device.

The Vishay Siliconix Si4642DY SkyFET device was tested against competing single-chip MOSFET/Schottky devices as well as industry-standard discrete MOSFET and Schottky diode combinations using the same controller IC and high-side MOSFET. The circuit using the SkyFET device performed with greater efficiency, whether in a light or heavy load condition, according to Vishay. For example, efficiency greater than 91 percent was demonstrated at 300kHz and 6A. These benefits are the results of the low forward voltage drop and reverse recovery charge of the Si4642DY's integrated Schottky diode and the reduced PCB parasitic inductance enabled by the integration of both devices onto a single chip, said Vishay.

The Si4642DY SkyFET power MOSFET diode will typically be used as the low-side power MOSFET in synchronous buck converters for notebook core voltage and VRM applications, graphic cards, point-of-load power conversion, and synchronous rectification in computers and servers. The device combines a 30V breakdown voltage with a MOSFET on-resistance of 3.75m at a 10V gate drive.

Integrating the Schottky diode with the MOSFET on a single chip saves board space but also improves device performance compared to using separate or co-packaged components, said Vishay. First, the forward voltage drop (VF) across the Schottky diode is much lower than the voltage drop across the intrinsic body diode of the MOSFET. This results in substantially less power loss when the MOSFET is turned off during dead time in a buck converter application, said Vishay.

A second improvement results from the lower reverse recovery charge (QRR) of the Schottky diode compared to the QRR of the body diode of the MOSFET. QRR is reduced by almost 20 percent, which improves converter efficiency at light loads, said Vishay.

In addition, the integration of the Schottky into the MOSFET silicon chip eliminates the parasitic inductances that would be present if these were mounted to the PCB as individual components or if separate MOSFET and Schottky diode components were co-packaged. The result is higher efficiency and smoother waveforms, as well as a 55 percent lower on-resistance at 4.5V compared to an equivalent co-packaged MOSFET/Schottky device, according to the company.

Availability: Samples and production quantities of the Si4642DY are available now, with lead times of 8 to 10 weeks for larger orders.

- Gina Roos

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