Dealing With Nonlinear MOSFET Capacitances

Focus:

Originally developed for high-voltage devices that resulted in superjunction MOSFETs, charge balancing is now getting extended to lower voltages as well. While it reduces both RDSON and all the junction capacitances dramatically, charge balancing makes the latter much more nonlinear as a function of voltage. The effective stored charge and energy in the MOSFET is indeed reduced, and significantly so, but calculating these parameters or comparing different MOSFETs for optimum performance has become a rather complicated exercise. As a result, the conventional approach to understanding MOSFET parameters such as COSS and CRSS is no longer valid. This article explains why and presents some guidance on how to better evaluate a MOSFET’s performance within its operating environment based on principles of stored charge and energy. Some attempts to analyze the nonlinear MOSFET capacitances are briefly discussed. Article also includes an extensive set of references.

What you’ll learn:

• How to evaluate and compare MOSFET capacitances when designing power converters

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Author & Publication:

Sanjay Havanur, Vishay Siliconix, Santa Clara, Calif., How2Power Today, Mar 15 2017

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