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• Enabling Future Innovations: Intermediate Bus Converter—Part 2: Performance

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Figure 1

   

Abstract

Converting 54 V to a suitable 12 V is a challenging task that requires a new converter topology to develop an improved, high performance power supply. Additionally, it must have small dimensions to fit into the latest data center and hyperscale architecture, making a quarter brick small form factor highly desirable. This article will explore how an Analog Devices’ reference design stands out by addressing key concerns such as efficiency, power loss, thermal dissipation, and common footprint design. It will also discuss how the benefits and advantages can impact system applications.

Introduction

In today’s world of digital information and constant social connection, having a well-designed and efficient data center is essential. These data centers provide the networking, storage, and global connectivity we rely on. Keeping them running smoothly is crucial to avoid data interruptions and corruption. However, older data centers are struggling as they are operating near their limits with the market’s increasing demand of computing power, and their usage is continuously increasing rapidly every year. For example, the use of artificial intelligence as a large language model in terms of weekly active users has doubled in less than a year. This has led to a growing need for higher power density, which in turn will need more robust and high performance power converters.

As data centers scale up to support more powerful servers, networking equipment, and storage systems, they require higher power, which involves several stages of power conversion from the power transmission line down to the usable DC voltage level inside the rack. The legacy architecture in data centers is converting a rectified AC voltage down to 12 V DC, which will be the main power source inside the motherboards. However, 12 V DC architecture is becoming inefficient for main power delivery within the board. Increasing the input voltage to a 48 V supply allows for up to a 16× reduction in I²R losses across the PCB with considerably lower conversion losses and within the safety extra low voltage (SELV) level. 

Therefore, an intermediate bus converter is a critical component in modern data center power architectures, which converts a 48 V voltage bus line from the primary power source, such as an uninterruptible power supply (UPS), to the existing intermediate bus voltage (5 V, 12 V architecture) and point-of-load (POL) regulators. This power supply is called an intermediate bus converter (IBC). IBCs come in various power capacities and sizes, with one common type being the quarter brick (QB) power supply.

A quarter brick power supply (QB PS) is a compact, efficient type of DC-to-DC converter module that plays a crucial role in modern power systems. It takes a high voltage DC input and converts it to a lower voltage that is ideal for powering a variety of peripherals and core processors inside the motherboard. The term quarter brick refers to its small, rectangular shape. These power supplies usually measure around 58.4 mm × 36.8 mm (2.3 inches × 1.45 inches) in a PCB area, with a height typically about 14.5 mm (0.57 inches). Despite the small size, a QB PS is highly efficient and can be easily integrated into existing power systems.

These power supplies are widely used in data centers, where their compact footprint and high efficiency make them ideal for use in server racks, network switches, ventilation systems, rectifiers, and battery backups. Their versatility and reliability make them a go-to solution for meeting the power needs of a modern electronic infrastructure. These power supplies usually operate with input voltage ranges of 40 V to 60 V, although there are variations available for different input voltages. They utilize a switching technique to efficiently regulate and convert the input voltage to a lower, regulated output voltage, typically from 9 V to 16 V. The output voltage can vary depending on the specific requirements.

Key Features of Quarter Brick Power Supplies Often Include:

High Efficiency

These power supplies are designed to maximize conversion efficiency. The reduction of conversion losses should be lower than the I²R losses a legacy 12 V DC architecture will incur.

Wide Input Voltage Range

They can accept a broad range of input voltages, making them compatible with various power sources. A typical nominal input voltage range falls within 48 VDC to 54 VDC with an extended range of 40 V DC to 60 V DC.

Protection Mechanisms

They incorporate protective features such as overvoltage protection, overcurrent protection, short-circuit protection, and thermal shutdown to safeguard the power supply and the connected devices.

Thermal Management

Efficient heat dissipation is crucial for reliable operation. QB power supplies often include thermal management features such as heat sinks or integrated fans to regulate temperature.

Remote Sensing

Some models support remote sensing, which compensates for voltage drops along the output cables, ensuring accurate voltage regulation at the load.

PMBus^® and Advanced Control Features

Many QB power supplies offer advanced control capabilities, such as voltage trimming, remote on/off control, and synchronization with other power modules.

Scalability

The QB power supply should be easily scalable with minimum circuit adjustment, can be configured in parallel operation for different power demands, and can handle pre-biasing startup for hot swap capability.

When selecting a QB power supply, it is essential to consider factors such as input/output voltage requirements, load current, efficiency, operating temperature range, and specific industry certifications or standards applicable to your application. These features are available in a QB reference design, which is suitable for demanding applications that require stable and efficient power delivery.

The key components of a QB power supply include an input filter, an output filter, some feedback control circuitry, and protection mechanisms that may be included in controller or power management ICs (PMICs). See Figure 1.

Advantages of a QB Power Supply

Compact Size

One of the primary advantages of a QB power supply is its compact form factor, which allows for efficient space utilization in applications where size is a constraint.

High Power Density

Despite their small size, QB power supplies offer high power density, enabling them to deliver significant power outputs.

Efficiency

With advancements in power conversion technologies, QB power supplies achieve high efficiency levels, reducing energy wastage and minimizing heat dissipation.

Thermal Management

QB power supplies often incorporate thermal management consideration, such as a flat baseplate that can be extended with a heat sink to ensure optimal operation and reliability in challenging thermal environments.

Reliability and Durability

These power supplies are designed to meet stringent industry standards, ensuring long-term reliability and durability even in harsh operating conditions.

Supply Resiliency

QB power supply pins are compatible between different manufacturers due to their common footprint package (CFP) to ensure resilient supply chain in production or ease of after-sale support in case of field failures.

Key Features of the QB Power Supply

Wide Input Voltage Range

QBM power supplies typically support a wide input voltage range, allowing for compatibility with various power sources.

Output Voltage Regulation

They provide precise and stable output voltage regulation, ensuring consistent performance across different load conditions.

High Power Density

This quarter brick design is capable of delivering 2 kW on regulated 12.2 V for the same off-the-shelf quarter brick power supply.

Scalable

The topology is a current-mode power supply that can easily be paralleled by tying its soft start pin and compensation pin together. This reduces the complexity for parallel operation. Figure 2 shows an example of how each QB can be paralleled.

Protection Mechanisms

QB power supplies incorporate protection features such as overvoltage protection (OVP), overcurrent protection (OCP), short-circuit protection (SCP), and thermal shutdown to safeguard against electrical faults and prevent damage to connected devices.

Coupled Inductors in Intermediate Bus Converters

A coupled inductor is another excellent technology to incorporate a quarter brick power supply for intermediate bus applications due to the integer ratio conversion. A 48 V to 12 V conversion will have 50% duty cycle, which makes the buck section operate at a notch for a 2-phase coupled inductor design. Even for a wider 40 V to 60 V (typical) input voltage range, it can still benefit from using a coupled inductor instead of a discrete inductor (DL). Figure 3 shows the normalized current ripple comparison between a discrete inductor and coupled inductor with different phases.

As seen in Figure 3, the current ripple is minimized at 50% duty cycle for a 2-phase coupled inductor design. Notice that the benefit of coupled inductors is not the same across different duty cycles. Different phases have different notch locations where the reduction of current ripple is maximized. So, it is important to consider the input voltage range and target output voltage of the quarter brick design. For example: a buck converter with a 4:1 step-down ratio should use a 4-phase design to maximize the coupled inductor’s current ripple reduction. See Figure 4 for an example of a single 4-phase coupled inductor.

The most important impact of using a coupled inductor in a quarter brick design is its significant reduction in the size of magnetic components, which is required for quarter brick PCB dimensions. The use of a coupled inductor allows for delivering high output power at competitive efficiency.

Applications of Quarter Brick Power Supply

QB power supplies find applications in various industries and sectors, including the following.

Telecommunications are commonly used in telecom infrastructure, data centers, and networking equipment to power communication systems and network switches.

QB power supplies are suitable for industrial automation applications such as motor drives, robotics, and control systems.

Using a quarter brick power supply is suitable for different output voltage step-down ratios. ADI’s discrete quarter brick reference design makes it easier to include multiple coupled inductor footprints available to evaluate up to two different output voltage levels, or parallel them together to test at higher output current requirements. See Figure 5 for the quarter brick section.

Conclusion

Older data centers are struggling to meet the increasing demand for computing power, especially with the rapid growth of artificial intelligence. To address these challenges, modern data centers are adopting new designs with higher power density, such as the 48 V architecture, which significantly reduces power losses compared to the traditional 12 V architecture. A key component in this transition is the intermediate bus converter, specifically the quarter brick power supply. These compact, efficient DC-to-DC converters are essential for converting high voltage DC input to lower voltages required by various peripherals and core processors.

The QB power supplies provide a streamlined, high performance power solution suitable for diverse applications. Renowned for their compact design, energy efficiency, and robust reliability, these power supplies boast superior power density, accurate voltage regulation, and advanced protective features, making them an essential component across various industries. They are designed to maximize space utilization, ensure reliable operation, and meet the power needs of modern electronic infrastructure.

Analog Devices’ quarter brick power supply delivers key advantages for powering data centers while offering high efficiency, robust performance, and advanced control features. Enhanced reliability and reduced operational costs make it an ideal solution for efficient and dependable data center power management.

The next part of this series will discuss the comprehensive evaluation for the quarter brick power supply and the data gathered to provide the electrical and thermal performance, as well as the proper component selection for high power application.

References

Ben-Yaakov, Sam and Michael Evzelman. “Generic and Unified Model of Switched Capacitor Converters.” 2009 IEEE Energy Conversion Congress and Exposition, September 2009.

Cruz, Christian. “The Power of 48 V: Relevance, Benefits, and Essentials in System-Level Applications.” Analog Dialogue, July 2024.

Evzelman, Michael and Shmuel Ben-Yaakov. “Average-Current-Based Conduction Losses Model of Switched Capacitor Converters.” IEEE Transactions on Power Electronics, Vol. 28, No. 7, October 2012.

Haug, Bruce. “72 V Hybrid DC-to-DC Converter Reduces Intermediate Bus Converter Size by up to 50%.” Analog Dialogue, February 2018.

Ikriannikov, Alexandr. “The Benefits of the Coupled Inductor Technology.” Maxim Integrated, March 2015.

Ikriannikov, Alexandr and Laszlo Lapcsei. “Greatly Increase the Efficiency of the Regulated 48 V to 12 V First Stage.” Analog Devices, Inc., December 2023.

“OpenAI says ChatGPT’s Weekly Users Have Grown to 200 Million.” Reuters, August 2024.

Webb, Samuel and Yan-Fei Liu. “A Novel Intermediate Bus Converter Topology for Cutting Edge Data Center Applications.” Chinese Journal of Electrical Engineering, Vol. 6, No. 4, December 2020.

About the Authors

Karl Audison Cabas

Karl Audison Cabas is an applications engineer focusing on power applications at Analog Devices since September 2020. He holds a bachelor’s degree in electronics engineering from Polytechnic University of the Philippines a...

Christian Cruz

Christian Cruz is a staff applications development engineer at Analog Devices, Inc., Philippines. He holds a bachelor’s degree in electronics engineering from the University of the East in Manila, Philippines. He has more ...