Vishay’s Monolithic SkyFET™ Power MOSFET and Schottky Diode Enables 6% Improvement in DC/DC Converter Efficiency
The new 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. For example, efficiency greater than 91% 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.
The new Si4642DY SkyFET power MOSFET 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 new device combines a 30-V breakdown voltage with MOSFET on-resistance of 3.75 milliohms at a 10-V gate drive.
Integrating the Schottky diode with the MOSFET on a single chip not only saves board space but also improves device performance in three major ways compared to using separate or copackaged components.
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.
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. Vishay Siliconix SkyFET technology reduces QRR in the device by almost 20% from the standard MOSFET body diode, which improves converter efficiency at light loads.
Finally, 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 for the Si4642DY is higher efficiency and smoother waveforms, as well as a 55% lower on-resistance at 4.5V compared to an equivalent co-packaged MOSFET/Schottky device.
Samples and production quantities of the Si4642DY are available now, with lead times of 8 to 10 weeks for larger orders.
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