Electronicdesign 4966 Xl cissoid

High-Temp Isolated Gate Driver Eyes SiC, GaN Devices

Nov. 9, 2011
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Mont-Saint-Guibert, Belgium: Welcome to Hades. At least that’s what Cissoid implores regarding its isolated gate-driver solution designed to drive high-temperature power transistors—specifically (but not exclusively) silicon-carbide (SiC) and gallium-nitride (GaN) fast-switching devices. It operates reliably at the same temperature as the switches (200°C junction and above).

The Hades platform comprises a reference design and an evaluation board that can drive low-switching-loss SiC power transistors, and switch them at high frequencies. That ultimately translates into smaller and lighter passive and magnetic components.

“The board has been designed to support fast switching and high frequencies up to 150kHz,” says Jean-Christophe Doucet, Cissoid’s vice president of marketing & business development. “The limitations come from the MOSFETs—dynamic losses increase the temperature and the MOSFET blows up. In the future we will develop our own MOSFET for high temperature operation.”

Thanks to its ability to sustain high temperatures, Hades can be located alongside the power transistors. As a result, it reduces parasitic capacitances and inductances, which further improves the associated losses and delays in the system.

According to the company, higher-efficiency power converters that are five times smaller and lighter than before can now be developed. Such converters will also be able to operate in high ambient temperatures. No matter what the temperature, though, the system’s lifetime will be an order of magnitude longer than traditional solutions.

Hades can drive two SiC MOSFET power switches on a dc bus voltage up to 1200V. The reference design is scalable up to ±20A gate current, while the evaluation board features ±4A. A specific board flavour for normally-on JEFTs will also be available, and other types of switching devices (normally-on/off JFETs, BJTs, and IGBTs) can be supported by making a few minor changes.

As an example, Hades’ operation and performance were demonstrated in a 3kW buck dc-dc converter, driving SiC MOSFETs, at 175°C ambient and switching at 150kHz (rise times were less than 25ns). In these operating conditions, it runs with comfortable safety margins. Generally speaking, Hades is designed for high dV/dt immunity (50kV/μs) and IC junction temperatures up to 225°C.

In terms of efficiency, combining Hades with the newest SiC switches in advanced power-converter topologies should bring efficiencies in excess of 98%, even at switching frequencies above 100kHz.



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