Texas Instruments (TI) has launched a 650V Gallium Nitride (GaN) FET with a silicon driver in the same package for industrial designs.
The GaN transistor operates as an ideal diode rather than depletion or enhancement mode to simplify the design and management of flexible, high power systems up to 5kW in a QFN package. “This is a milestone not just for TI but for GaN in general that the technology has reached this level,” said Steve Lambouses, Vice President & GM of High Voltage Power at TI.
The combination has been under test with customers since 2018 to gather 40m hours of reliability data before the launch. “The discussions now are not about reliability, they are about how to optimise the system, optimise the topologies, how to use the ideal diode mode, the digital reporting, that’s what’s exciting and very different from the earlier days of GaN,” said Lambouses.
“For every 1W you save in efficiency you can save 1W in cooling so you get a magnifying effect in reducing losses,” he said. “When you think about switching 5kW in a QFN package that’s unique, the thermals and the technology that has to come together in a low profile package. It’s combining the package with the low inductances for the switching speed. 5kW has been possible for a long time but in large packages. This combination comes from putting the silicon driver in with the GaN to provide the power with a small volume.”
The driver in the LMG340x supports a switching frequency of 2.2MHz for 99 percent conversion efficiency. This higher frequency also reduces the size of the magnetics by 56%, reducing the size and weight of onboard chargers and inverters. The on-resistance of 30 mΩ of the epitaxial lateral GAN FET reduces the thermal losses and the size of the heatsink required.
“You don’t see integrated driver and controller at these power levels,” he said. “It’s uniquely different in terms of reliability. If you are really going to take advantage of the 50 percent reduction in size or the elimination of the fan, that’s a complete redesign of the system, re-architecting a smaller, cheaper system. That’s the discussion that has been going on for a while and has to go through qualification and reliability testing and that’s where customers are at today,” he said.
“This provides twice the power output in a 1U rack server up for 1.2kW to 2.8kW in the same form factor and to do that you need to be really efficient,” he said. “The same applies for 5G, putting a small cell on top of a lamp post. We have customers that have gone from liquid cooling to forced air cooling, or from forced air to convection cooling as a result of the higher efficiency. It lends itself to better thermal performance and removes the fan which increases the reliability,” he added.
Lambouses says 650V is the sweet spot and doesn’t plan to support higher voltages. Higher voltage designs can be supported with the switches in parallel, synchronised by the controllers.
“We believe in this voltage – this is the area that GaN provides the most benefit,” he said. “Customers use this for 800V and 900V buses with a multi-level topology up to 1200V with higher efficiency and smaller heatsinks instead of using one larger FET,” he said.
The silicon controller in the package supports an ideal diode mode for the GaN switch. This mode is different from enhanced or depletion modes used in other GaN devices. This ideal diode mode allows optimization of the dead time in a switching topology for higher efficiency as the GaN FET is turned on automatically by the built in gate driver after a very short delay when a negative drain to source voltage is sensed.
“It’s still a switch so you can use in in many different areas,” said Lambouses. “We also see it in solar inverters, in places where the wave shaping in s important such as test and measurement and the low capacitance makes it ideal for those configurations. The integration of the controller and gate drive and the active power management, and monitoring, that’s a big difference.”
The controller also includes digital temperature reporting for active power management, allowing engineers to optimize system thermal performance under varying loads and operating conditions.
TI expects volume production next year. Top and bottom-cooled variants of the 12 x 12mm package are available.
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