White Paper Proposes GaN for Nvidia 800V Architecture

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Earlier this year, Nvidia announced that it would lead a consortium to develop an 800V DC power delivery system for data centres. The new architecture is required for the advanced data centres required to meet the increasing demand for AI services. Currently a 48V architecture is used as the power delivery bus, but the latest AI processors are far more power hungry than their predecessors and future generations will see that trend accelerate, giving a realistic expectation that individual racks will have power demands of 1MW and over. The aim of the new 800V architecture is to increase end-to-end power efficiency by 5% and reduce maintenance costs by up to 70%.

Silicon carbide or stacked GaN may seem to be the most realistic prospect to down-convert from such a large voltage, but according to Chris Lee, Director of Product Marketing, at Power Integrations, a single GaN conversion stage will offer the optimal solution. The company has been developing GaN solutions for higher voltage levels for many years, and currently offers 1250V solutions, as well as a low power 1700V device for auxiliary power supplies. It is the 1250V range that Lee sees as key to meeting the needs of the new 800V power delivery system, and he cites its qualification and use in automotive 800V architectures as proof that GaN has the ability to perform at high voltage levels in challenging environments.

Lee explains, “the automotive qualification process gives customers a level of confidence that PowiGaN has a proven record of reliability, and is suitable for deployment in the data centre’s tough working environment. We have a full reliability record, and not only from the automotive sector, PowiGaN is currently in use across many different application segments. We have written a new white paper which will explain the performance advantages of our 1250V PowiGaN 1250 HEMTs in detail and compare it with 650V stacked GaN and silicon solutions, as well as single 1200V SiC architecture.”

According to Lee, the cascode configuration of the PowiGaN switch provides a huge advantage for this type of application. It allows the switch to be tightly controlled, and it has no need for a negative voltage input, bringing safer turn-off behaviour. The cascode device also offers a safer area of operation, with PowiGaN able to switch comfortably from 0V to 10V with breakdown starting around 25V. Tight control over the switching also allows a much shorter dead time.

Most alternate solutions do not use cascode configurations. To ensure efficiency is as high as possible, switching speeds need to be very fast, and the complications of driving several transistors in sync at that rate, make using external drivers very complex.

Lee expanded by saying, “driving these types of applications is always a challenge. You have to design your driver into the package or it will be very difficult to control the switch. External drivers have to cope with a gate threshold voltage that is within a very narrow range for the e-mode GaN, particularly when they are normally off and running at a high frequency. Every cycle, you need a positive voltage to turn it on and then a negative one to turn it off, and that has to be done very quickly and in perfect synchronization with the other switches in the circuit. If you're using parallel GaN stacks running in three phases, that creates a huge complexity. The absolutely maximum voltage to turn the switch on is around 7V and beyond that there is a risk of failure. These are very narrow margins.”

He continued, “Using 1200 V SiC can be done, but then you completely ditch the benefits of high frequency switching. If a small solution is required, and data centres are looking for the most power dense solutions, you need smaller magnetics, and that usually means a planar transformer. The highest frequencies possible are necessary to enable that. The solution detailed in the white paper also outperforms the SiC solution in efficiency, leading to fewer thermal issues”.

The proposed architecture detailed in the new white paper also highlights the capabilities of the company’s 1700V GaN device, integrated in the InnoMux2-EP IC, as a primary side auxiliary power supply to power fans, pumps or any other devices required. The device’s synchronous rectification ZVS operation provides an efficiency of over 90.3% converting directly from 800V to 12 V.

The white paper can be downloaded here https://www.power.com/ai-data-center