Enabling Future Innovations: Intermediate Bus Converter—Part 2: Performance
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Abstract
A quarter brick power supply is a critical component in data center applications with the emergence of 48 V architecture. It must offer high performance in terms of efficiency and transient requirements while maintaining its size within a quarter brick form factor. The quarter brick power supply shows that both the efficiency and transient requirements can be designed in such strict form factor constraints while delivering industry-leading output power of 2 kW. The reference design shows 98.59% peak efficiency at 48 V input, and 97.68% efficiency at full load for 54 V input.
Introduction
With the development of stronger processor cores and the increasing usage of artificial intelligence (AI) chips in data centers, the power requirements for next-generation machines are greater than their predecessors. These machines need to maintain their form factor to ensure that the upfront cost for migration is minimized. Therefore, a better-performing power supply of the same dimension is in demand to provide the next generation of chips with the required power. This is why using a standardized quarter brick power supply is advantageous for system design. Using a quarter brick power supply reduces system design complexity because of its ready-to-use features and compatibility among different vendors.
However, quarter brick power supplies do not have the same topology nor performance, so engineers should choose carefully depending on their requirements. Operating input voltages, output voltage regulation, peak and full load efficiency, transient and thermal performance, and scalability are some of the key parameters that engineers should consider when designing with a quarter brick power supply.
This article will discuss the performance of a discrete quarter brick power supply and how it meets a higher output power requirement with very high efficiency.
Data and Results
The test findings below comprise of start-up and steady-state performance measurements, functional performance waveforms, and temperature measurements. The following configurations were tested using the quarter brick reference design and its system board. The system board is equipped with a hot swap circuit.
QB Power Supply Operation Settings
- Input Voltage: 40 V to 60 V
- Output Voltage: 12 V
- Output Load: 0 A to 166.67 A
- Switching Frequency: 150 kHz
Performance Data
Efficiency and Power Loss
Using a 4-phase DC-to-DC converter lowers the current per phase, therefore reducing conduction losses. The quarter brick is tested at 48 V and 54 V input for efficiency and is plotted in Figure 1. At lower input voltage, peak efficiency is greater due to lower step-down voltage. However, it slowly rolls off at higher output power due to increasing input current. Conversely, lower peak efficiency is seen at 54 V but has better full load efficiency.
In a quarter brick PCB area, the converter achieves about 98.59% of peak efficiency at 48 V, 800 W, and full load efficiency of 97.33%. For 54 V applications, it can achieve a peak efficiency of 98.45%, 1000 W, and 97.68% at full load.
The synchronous rectification employed mitigates diode conduction losses, further optimizing efficiency. By utilizing high quality, low equivalent series resistance (ESR) input and output capacitors, along with proper coupled inductor selection, losses across critical components are reduced. This meticulous component selection and design considerations contribute to overall power loss reduction.
With proper layout design, thermal management, and optimization of control loop parameters, the device enables reliable and efficient power supply solutions.
Transient Response: Extended Power Delivery
The converter is well-suited for dynamic power delivery requirements for intermediate bus applications. Its 4-phase architecture enables efficient load distribution, reducing the effects of unexpected changes in load circumstances. This design innovation improves with the controller’s capacity to adapt to shifting power needs rapidly and effectively, ensuring a constant output voltage during transient occurrences. The interleaved operation allows for a quick response to sudden load fluctuations. This responsiveness is critical in situations where quick power supply adjustments are required.
It is designed to deliver extended power for a limited amount of time to support sudden load demands while maintaining the regulated output voltage. This 2 kW rated design was tested for 1.5× extended power delivery for 50 ms as seen in Figure 2, and 1.8× extended power delivery for 500 µs as seen in Figure 3.
The transient response of the converter can be further optimized by tuning its type-2 compensation, enabling precise regulation, and minimizing deviations in the output voltage.
Thermal Performance
The thermal performance of this reference design is a critical factor of its overall functionality. Proper thermal management ensures the reliable operation of the device and prevents overheating, which can degrade performance and shorten the lifespan of electronic components. See Figure 4 for its thermal characteristics without the heatsink and baseplate implemented.
Enhancing the thermal performance of the quarter brick power supply by incorporating effective heatsinking ensures thermal dissipation while maintaining adequate airflow around the device. The data sheet typically provides recommendations for proper heatsink design, including details on thermal resistance and the maximum allowable junction temperature. By implementing these guidelines, designers can prevent the critical devices (controllers, FETs) from exceeding temperature limits, ensuring reliable and continuous operation. Additionally, the converter includes features such as overtemperature protection, which helps safeguard the device against thermal issues. This protection mechanism can automatically shut down the controller or reduce its output power in the event of excessive temperatures, preventing damage to the device and the surrounding components.
Start-Up Response
Startup allows for low input inrush current from the main power source to charge the bulk capacitors, and a gradual increase in the output voltage during the initial power-up phase. This prevents inrush current and voltage overshoots, enhancing system reliability and protecting downstream components from potential damage. The controller also includes fault monitoring mechanisms to detect abnormal conditions during startup, triggering appropriate responses to prevent potential issues. Figure 5 shows the start-up response before the output voltage ramps up.
During startup, the converter carefully ramps up the output voltage, ensuring a smooth transition to operational mode. This controlled approach is essential in applications where sudden changes in voltage could impact connected components. The controller is designed to handle startup under various conditions, accommodating a wide range of input voltages and load scenarios. For Analog Devices’ quarter brick reference design, the hot swap controller LTC4287 is also incorporated to ensure smooth input voltage ramp.
Output Ripple
Output ripple refers to the fluctuations or variations in the output voltage of the power supply. The converter achieves low output ripple by employing an interleaved phase with coupled inductor, where the switching phases operate slightly out of phase with each other. This phase interleaving effectively reduces output voltage ripple, providing a cleaner and more stable output voltage. See Figure 7.
The converter with output ripple performance is influenced by various factors, including the quality of input and output capacitors, the inductor selection, and the overall layout design. By using high quality, low ESR capacitors and properly chosen inductors, designers can further minimize output ripple. The data sheet typically provides guidelines and recommendations for selecting appropriate components to optimize output ripple performance. In applications where low output voltage ripple is critical, the multiphase design and features contribute to maintaining a smooth and precisely regulated output. This is particularly beneficial for powering sensitive electronic components or systems where stable voltage levels are essential for proper functionality.
Ripple data from both input and output voltage is also dependent on measurement setup so a short probe at the closest ceramic capacitor is recommended to capture the real ripple performance at steady-state.
Conclusion
Quarter brick 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 device across various industries.
ADI’s latest discrete intermediate bus converter delivers key advantages for powering data centers, offering high efficiency, robust performance, and advanced control features. Its ability to optimize power delivery, enhance reliability, and reduce operational costs makes it an ideal solution for efficient and dependable data center power management.
References
Cruz, Christian. “The Power of 48 V: Relevance, Benefits, and Essentials in System-Level Applications.” Analog Dialogue, Vol. 58, July 2024.
Haug, Bruce. “72 V Hybrid DC-to-DC Converter Reduces Intermediate Bus Converter Size by up to 50%.” Analog Dialogue, Vol. 52, February 2018.
Ikiriannikov, Alexandr and Laszlo Lipcsei. “Greatly Increase the Efficiency of the Regulated 48 V to 12 V First Stage.” Analog Devices, Inc., October 2023.
“The Benefits of the Coupled Inductor Technology.” Maxim Integrated, March 2015.
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