Renesas Electronics published a white paper on September 25, 2025, regarding the evolution of data center power systems. To address the power demands of surging AI workloads, the report advocates for an 800V High Voltage Direct Current (HVDC) power architecture.

Co-authored by Pietro Scalia, Yong Perry Li, and Ashish Ekbote of Renesas Electronics, the white paper integrates market strategy, device R&D, and engineering implementation to form a comprehensive "Technology-Product-Market" iron triangle.

The explosive growth of AI has led to a dramatic surge in data center IT rack power consumption, which now reaches hundreds of kilowatts. Consequently, the industry is transitioning from traditional 48V architectures to 800V HVDC architectures. By leveraging Gallium Nitride (GaN) technology, high power density and high-efficiency 16:1 step-down conversion can be achieved. Renesas Electronics is collaborating with NVIDIA to develop a new 800V architecture specifically for data center applications.

The contents feature the 16:1 800V DC/DC converter design in Chapter 3, the 64:1 800V converter expansion in Chapter 4, and the front-end PFC converter in Chapter 5.

Data centers are facing a major overhaul due to the surge in AI hardware. xPU and ASIC vendors are launching new technologies in rapid cycles, with spending far exceeding traditional server refreshes, drawing active involvement from semiconductor suppliers in this hardware shift.

Rapidly increasing xPU power needs are expected to push rack power to hundreds of kilowatts in the next year—over twice the level of today's GB300. The appetite for AI compute is now officially outstripping Moore’s Law.

Sticking with traditional 48V distribution leads to huge power losses or an over-reliance on heavy copper busbars. To handle the power spike, the HVDC approach delivers 800V DC directly to the rack, saving on copper.

Renesas’ white paper highlights converter topologies for this shift, using bidirectional GaN switches in a Vienna topology. This setup simplifies the AC/DC front-end, cuts costs, and produces 800V DC with module power reaching 20kW or more.

Figure 1 illustrates the trend of maximum current for SoC power. The red scatter points indicate that the maximum current for AI GPUs, TPUs, xPUs, and networking ASICs is growing exponentially, with a predicted peak potentially exceeding 4000A by 2028. In contrast, the blue scatter points represent traditional x86 and ARM CPUs, which show moderate power growth, peaking at 1000A.

By implementing a Side Car architecture, the AC/DC conversion units are moved out of the compute rack and placed into a dedicated Side Car rack. Power is delivered to the compute rack via 800V HVDC, which reduces copper usage and enhances power density. Within the compute rack, a 16:1 LLC topology is employed to step down the voltage to 48V to power GPUs and xPUs.

GaN devices support high-frequency conversion at MHz levels with manageable losses, allowing for the compact, high-density designs needed for modern racks. Using a DC transformer to step down to 48V ensures compatibility with the current 48V ecosystem.

These converters also enable a 64:1 ratio, stepping 800V directly down to 12V and skipping the 48V intermediate stage. Another option is using a GaN-based eight-switch hybrid capacitor converter to reach 6V.

With GPU power demands reaching the kilowatt range, Vertical Power Delivery (VPD) is being used to cut distribution losses. VPD requires low-profile, highly integrated modules. The final stage of conversion is then handled by high-frequency integrated voltage regulators.

Renesas is utilizing its expertise in GaN/Si switches, digital controllers, and PoL/BMS technology to help OEMs and hyperscalers build the next generation of power architectures.

Figure 3 displays Renesas’ power portfolio for AI data centers. As GPU demands push server power from 20-30kW to more than 130kW, the industry is moving toward high-voltage busbars and Side Car rack designs, which can scale up to 1MW.

The current Renesas lineup includes 4th Gen digital multiphase controllers, 3rd Gen smart power stages, high-density vertical power modules, and specialized optimization software. It also covers 48V isolated converters, DDR5 PMICs, and 16-cell battery management solutions.

Upcoming products feature GaN transistors, eFuses, and a range of next-gen MOSFETs and drivers.

Figure 5 illustrates the HVDC DC/DC conversion architecture for next-generation racks, utilizing an 800V DC bus input with two 3kW half-bridge LLCs to convert 800V to 48V. It introduces Renesas’ GaN switches, drivers, and digital power controllers optimized for this circuitry.

In alignment with Open Compute Project principles, the content of this topic is generated following OCP guidelines. Its mission is to showcase a standardized and open topological approach to address the challenges of new architectures and to inspire industry-wide adoption. This yields a significant impact on copper savings in IT racks and enhances overall efficiency from grid to core, enabling the sustainable implementation of IT infrastructure.

This DC/DC methodology has been validated at a 12kW power level within a full-brick form factor, offering the scalability to withstand potential power fluctuations. Furthermore, by transitioning from 48V to even lower intermediate voltage values, it can further improve the overall efficiency and power density of blades and the racks themselves. The technologies and components involved in these new architectures are also applicable to Side Car AC/DC racks, where GaN BDS and UDS devices can enhance efficiency and reduce costs through simplified topologies.

Designed for IT racks, this 16:1 800V DC/DC converter system utilizes two parallel 6kW units. Within each unit, two 3kW 400V-48V LLC modules are employed. By configuring inputs in series and outputs in parallel, the design optimizes power density and transformer efficiency while remaining adaptable to different power requirements.

In the emerging high-voltage DC architecture, the 48V and 12V outputs do not require regulation by the power supply, as downstream low-voltage DC/DC converters handle the task of providing regulated DC voltage to the GPU. The elimination of the need for output voltage regulation makes this architecture ideally suited for the LLC DCX (DC-Transformer) mode.

To achieve regulation, traditional LLC converters must vary their switching frequency, requiring closed-loop control algorithms and high-speed ADCs for real-time sampling. In contrast, LLC DCX operates at a fixed frequency with open-loop control, removing the need for high-speed ADCs and real-time control complexity.

Matrix transformers differ from conventional designs by interconnecting multiple windings around a single core, delivering exceptional power density and efficiency. By integrating windings directly into the PCB, it allows for a tight, synergistic design of synchronous rectification and output capacitors. Figure 8 showcases the LLC DCX with a matrix transformer, integrating the controller, drivers, and FETs into a streamlined PCB layout.

The 3kW 400V-48V DCX building block uses a half-bridge LLC topology. For the primary side, Renesas TP65H030G4PRS GaN switches in TOLT packaging offer top-side cooling for easier thermal design. The secondary side employs a two-phase full-bridge setup with Renesas RBE024N08R1SZN6 synchronous rectifiers.

A Renesas RA6T2 MCU manages PWM control, synchronous rectification, and fault handling. Since it runs as an open-loop system with a fixed ratio, no real-time control is required. A single MCU on the secondary-side ground generates the PWM signals for both sides of the converter.

Figure 9 illustrates the gate drive scheme for the 3kW 400V-48V LLC DCX module. The primary side utilizes isolated high-voltage gate drivers to ensure safety and signal integrity. On the secondary side, the Renesas HIP2211 100V half-bridge gate driver is employed to simplify the low-voltage side design, while a matrix transformer is used to achieve high-power density integration.

In HVDC systems, the auxiliary power supply not only provides power to the MCU, gate drivers, and peripherals but also manages the sequencing for the 800V DC bus connection and disconnection. The Renesas iW1825 flyback converter, which integrates both the switch and controller, utilizes primary-side regulation (PSR) technology to simplify design and enhance reliability.

Planar matrix transformers are ideal for ultra-high power density applications, as their integrated structure ensures uniform flux distribution and reduces core losses. Renesas has completed the design, prototyping, and testing of the 3kW 400V-48V LLC DCX and is continuously optimizing the unit to further reduce its footprint.

Figure 10 illustrates the simulation results for the 3kW 400V-48V LLC DCX prototype. Using Ansys 3D magnetic simulation, the view shows the flux density distribution within the uniform air-gap transformer design. With a switching frequency of around 650kHz, the LLC DCX successfully implements primary-side ZVS and secondary-side ZCS.

The test waveforms for the prototype are shown in Figure 11: CH1 (blue) is the primary switch node voltage, CH2 (cyan) is the secondary transformer output voltage, and CH3 (purple) is the primary current.

For 800V-to-12V power delivery, a 64:1 converter uses an LLC DCX topology with an 8x secondary center tap. This approach lowers current stress on secondary-side synchronous rectifiers and cuts conduction losses to boost efficiency.

With a predicted efficiency of 96.7% at 3kW, the performance is just 1% shy of the 48V version. However, the true advantage lies in skipping conversion stages, which greatly simplifies the system architecture.

Figure 13 shows the primary resonant tank and secondary switching currents at 3kW full load. With the primary switch current (purple) and gate drive voltage (cyan) aligned, Zero Voltage Switching (ZVS) is attained, cutting down switching losses.

In Figure 14, at 3kW load, the output current (yellow) and voltage (red) are displayed, exhibiting a current ripple of about 14A and a voltage ripple of roughly 500mV.

The front-end PFC in the Side Car rack converts mains power to a stable 800V DC. The Vienna rectifier remains a popular choice for PFC, and by integrating bidirectional GaN devices, conduction losses are minimized. These bidirectional switches also streamline the drive circuitry, leading to even higher power density.

With a lateral structure, bidirectional GaN switches support both substrate and top-side cooling. The devices feature quasi-zero reverse recovery and rapid switching, which keeps switching losses at a minimum. By replacing two conventional switches with a single new bidirectional high-voltage GaN component, Renesas has shrunk the power stage size, boosted efficiency, and gained a cost advantage.

Megawatt-scale AI data centers require a shift to high-voltage architectures. The white paper covers modules for IT and Side Car racks using open, scalable methods. GaN's ability to cut switching losses and support higher frequencies simplifies designs and increases reliability.

Renesas showcased its 3kW 400V-48V LLC DCX converter design and results, proving through simulation that the architecture is ready to scale. More modules are currently in the works to test future design evolutions. Renesas is calling on data center OEMs and hyperscalers to partner with chipmakers in shaping the next generation of power delivery.

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Summary

The white paper details Renesas' 16:1 800V-to-48V DC/DC design, which operates in LLC DCX mode to simplify control by eliminating the need for regulation. Matrix transformers are employed to provide superior power density and conversion efficiency compared to traditional transformers. While the 64:1 800V-to-12V DC/DC design experiences a 1% efficiency drop relative to the 48V conversion, it reduces system complexity by eliminating the 48V-to-12V intermediate stage.

Furthermore, bidirectional GaN switches replace two conventional MOSFETs, making them ideal for Vienna rectifier applications in front-end PFC stages to reduce conduction losses, simplify driver design, and enhance power density with a cost advantage. The white paper also highlights Renesas' power portfolio for AI data centers, including digital controllers, smart power stages, vertical power delivery modules, 48V isolated converters, DDR5 PMICs, and 16-cell battery management solutions.