Smart Battery Backup for Uninterrupted Energy Part 5: Auxiliary Power System

Abstract

Part 5 of this article series explains the significance of auxiliary power within the Analog Devices battery backup unit (BBU) reference design. Auxiliary power encompasses supplementary voltage rails, provided alongside the primary power output, to bolster numerous components and functionalities. Its importance is paramount for ensuring the dependable and streamlined functioning of the power devices integrated into the BBU reference design module.

Introduction

Power supply units (PSUs) and BBUs serve as the lifeblood that feeds the functioning of data centers, networks, servers, and storage devices in the cutting-edge Open Compute Project (OCP) Open Rack Version 3 (ORV3) architecture. The central power converter is in charge of delivering the majority of required electrical energy. However, the unrecognized hero is the auxiliary power component, which plays a vital function in maintaining the overall robustness, dependability, and security of the entire power provisioning ecosystem, which includes both the PSU and the BBU.

In the following detailed discussion, we will conduct an examination of the role that auxiliary power plays within the BBU module’s reference design, exploring its functions and inner mechanisms. By delving into the intricacies of auxiliary power, we aim to highlight its substantial contribution to maintaining a continuous power supply and safeguarding our valuable technical resources from potential harm.

Standby Power

Auxiliary power is used to provide secondary power within a BBU. Even if the backplane power supply is disrupted or unavailable, supplemental power continues to power the devices inside the module, enabling the smooth functioning of key operations stored within the BBU. This standby power capability enables the unit to retain and sustain important operations such as a safe transition process, vigilant monitoring, complex control circuitry management, and consistent facilitation of low power devices. Auxiliary power ensures the modules’ capacity to distribute power when needed by providing a continuous uninterrupted power supply during power outages. This, in turn, acts as a buffer against potential disturbances and prevents data loss from occurring.

Voltage Regulation

Ensuring a state of constant equilibrium and constant voltage output is vital for achieving optimal performance of those devices inside the BBU. The importance of having auxiliary power in this scenario cannot be overstated, as it acts as a crucial protective measure, overseeing the sensitive area of voltage control inside the sophisticated architecture of a BBU module. Auxiliary power constantly monitors the output voltage, orchestrating adjustments and stabilization within the precise confines of a meticulously defined tolerance spectrum.

This regulation stands as a shield, enhancing the mutual interaction between the BBU and its associated devices. Auxiliary power ensures a steadfast and dependable energy source, safeguarding against voltage fluctuations that could otherwise trigger malfunctions, data corruption, or physical damage.

Auxiliary power becomes essential through its precise calibration. It not only keeps the module running efficiently, but it also protects the connected devices. This combination of precision and dependability paves the way for the PSU, BBU, and an array of associated devices in the data center to have a longer lifespan, increased efficacy, and enduring vitality of operation.

Cooling and Fan Control

Effective cooling management is crucial in preventing overheating in electrical equipment. Auxiliary power delivers and coordinates fans inside the BBU. This cooling process helps preserve the BBU and supported devices. This composition utilizes auxiliary power to manage fan revolutions and create a smooth and efficient cooling environment. The result is a well-balanced system that maintains optimal operating temperatures and protects against the damaging effects of overheating.

The dissipation of heat involves complex interactions within thermal dynamics. This system manages heat to prevent failures from overheating. Careful temperature regulation and auxiliary power increase performance and dependability.

Protection and Safety Features

BBUs feature a range of vital security and safety attributes, guarding both connected devices and the power converter. The integration of auxiliary power is pivotal in enabling these functions’ deployment and oversight. Auxiliary power empowers a spectrum of proactive measures, encompassing safeguards like overvoltage, overcurrent, and short-circuit protection, alongside temperature monitoring. This real-time vigilance by auxiliary power ensures swift responsiveness to anomalies or issues through continuous parameter checks. Such rapid activation of protective mechanisms effectively averts harm to the PSU and its connected devices, mitigating electrical hazards and notably enhancing the system’s overall safety.

Diagnostic Evaluation

The BBU conducts regular self-diagnostic tests to validate its functionality prior to supplying power to connected devices. In this process, auxiliary power furnishes the necessary voltage and control signals to initiate and conclude the diagnostic routine. This self-assessment aids in promptly detecting potential faults within the BBU, including component issues or voltage irregularities. Auxiliary power’s involvement contributes to the enhanced performance and prolonged life of the PSU by early identification and pinpointing of faults. This proactive approach elevates the reliability and preparedness of the PSU, ensuring uninterrupted power delivery and significantly diminishing the risk of system failures.

The power supply design tool, LTpowerCAD® from ADI, offers customized engineering insights and component performance data specifically designed for BBU auxiliary power. This powerful combination successfully expedites the complex process of electrical evaluation, speeds the prototyping phase, and adds a considerable acceleration to the overall development timetable for auxiliary power circuits. As a result, there is a noticeable reduction in the amount of time spent on review and the complexity of circuitry design.

In Figure 1, the image illustrates an auxiliary circuit designed to optimize energy flow during charge mode or discharge mode BBU operation, reflecting extensive engineering efforts. Conversely, Figure 2 shows a low power auxiliary circuit for BBU sleep mode, featuring low dropout (LDO) regulators and a single buck converter.

Figure 1. An auxiliary circuit design for a BBU module during charge and discharge operation.

Figure 1. An auxiliary circuit design for a BBU module during charge and discharge operation.

Figure 2. An auxiliary circuit design for BBU module during sleep mode.

Figure 2. An auxiliary circuit design for BBU module during sleep mode.

To power such power converters, microcontrollers, and other peripherals, the BBU module auxiliary circuit comprises six voltage rails as listed in Table 1.

Table 1. BBU Voltage Rails
During Charge or Discharge Mode Operation During Sleep Mode Operation
➤  12 V bias rail  
➤  5 V, 3.3 V, 1.8 V, and 1.2 V bias rail ➤  3.3 V, 1.8 V, and 1.2 V bias rail
➤  –3.0 V bias rail  

Auxiliary Power while in BBU Charge or Discharge Mode Operation

12 V Bias Rail

The LT8645S is a high voltage synchronous step-down controller with a remarkable load capability of up to 8 A. Its primary function is to efficiently convert the backplane voltage supply of 48 V into a 12 V auxiliary voltage supply, which it does with expert precision. The device’s integration of bypass capacitors differentiates it from other high voltage step-down controllers, a strategic choice that not only eliminates the need for a larger PCB footprint but also adeptly addresses difficulties such as rapid current loops and electromagnetic interference (EMI) emissions. This combination results in a significant increase in overall efficiency, enhancing the controller’s ability to optimize energy consumption.

The 12 V bias rail emerges as the support for fundamental components covering power converters, fan supplies, and current share bus circuits.By serving as the primary energy conduit for these critical components, the 12 V bias rail enables seamless operation and performance. The components are synthetically combined under a power source, with the LT8645 playing a crucial role in enhancing efficiency and functionality.

5 V, 3.3 V, 1.8 V, and 1.2 V Bias Rail

Employing the LT8692S, a quad-channel synchronous step-down controller, was a deliberate choice aimed at furnishing a diverse array of outputs: 5 V, 3.3 V, 1.8 V, and 1.2 V. This adjustment was particularly vital to adapt to the reduced auxiliary voltage, aligning with lower bus voltages. Guided by a singular oscillator operating at 2 MHz, the controller orchestrates its outputs with precision and synchronization.

What truly distinguishes the device is its integration of capacitors, a feature instrumental in meeting stringent EMI performance requirements by minimizing the layout’s susceptibility. This facet significantly enhances its compatibility with noise-sensitive settings and applications. The quad-channel architecture, marked by high integration, not only conserves space but also fosters a more concise and efficient design approach.

In order to explain how it’s used, the 5 V rails provide power for the amplifier rail supply, Modbus UART driver, digital temperature sensors, and power management device. The 3.3 V, 1.8 V, and 1.2 V outputs power the EEPROM device, main microcontroller unit (MCU), and battery management system (BMS) MCU, respectively.

–3.0 V Bias Rail

The LTC1983 is a wise choice of charge pump inverter since it provides a critical negative 3 V supply rail to the operational amplifiers driving the BBU. The device’s capacity to create a powerful 100 mA output load requires only a pair of additional capacitors, demonstrating its intrinsic efficiency. Notably, this efficiency is enhanced by its tiny form factor, a design feature that confers specific advantages—consummating its function with a mere 1 mm footprint on the power board of the BBU.

Auxiliary Power while in BBU Sleep Mode Operation

3.3 V, 1.8 V, and 1.2 V Bias Rail

The MAX17551 stands out as a synchronous step-down converter, transforming the battery stack’s 48 V voltage into a steady 3.3 V output. This voltage acts as a strategic conduit, channeling power to the digital general-purpose pins of both the main MCU and the BMS MCU while they are in sleep mode. This step-down converter was chosen due to its strengths: its versatility across input voltages ranging from 4 V to 60 V, its tiny and space-efficient form factor, and its outstanding operational efficiency, boasting a minimal draw of less than 10 mW. This convergence of characteristics puts it as the top solution for improving the overall durability and endurance of the battery stack.

The ADP165 LDO regulator achieves a more sophisticated voltage reduction, precisely lowering the supply voltage from 3.3 V to 1.2 V. This targeted reduction serves as the primary energy source powering the core operations of both the main MCU and the BMS MCU. Strategic integration of an LDO regulator within the microcontroller circuit enables improved voltage regulation, significant noise reduction, streamlined design architecture, superior operational efficiency, and an elevated standard of reliability. In addition, the ADP165 consumes less than 15 μW of power, making a significant contribution to the energy economy and, as a result, battery endurance.

Lastly, to power up the analog and USB supply voltage, and some other core voltages, the MAX38911 is utilized with its precise reduction of supply voltage from 3.3 V to 1.8 V. This LDO regulator can deliver up to 500 mA of load current, sufficient enough to provide the load current necessary for the microcontrollers. The power converter consumes around 19.2 μA of supply current in low power mode, making it suitable for sleep mode operation.

Emphasizing the significance of responsive thermal management cannot be stressed enough to maintain consistent optimal performance, given the auxiliary power supply’s remarkable efficiency result of 94% during charge or discharge operation while 62% during its sleep mode operation. The significance of selecting the best device for the auxiliary circuit goes beyond ordinary functionality; it forms the foundation of design integrity across the whole operating spectrum of the BBU. This strategic option predicts overall power use and computes the estimated battery lifespan. Furthermore, it allows for cost-effective possibilities for improving the auxiliary’s performance, culminating in a thorough improvement of the unit’s overall efficiency.1

Summary

In this final article of the series, auxiliary power is portrayed as a crucial component of BBUs that coordinates various important functions. Its function entails a number of key responsibilities, all of which are critical to the smooth, dependable, and secure running of these units. As the shield of standby power, auxiliary power adjusts voltage levels, manages the fan power supply for thermal cooling, deploys protective measures, and conducts power-on self-tests. This sophisticated interplay of operations converges to provide an uninterrupted power supply, protect our devices, and prolong the overall system’s vitality.

Auxiliary power is crucial for reliable and supplemental power to our analog and digital devices. Auxiliary power technology advancements are always improving efficiency, reducing power losses, and safety of data centers’ PSU and BBU, propelling innovation to new heights. This continuous progress is an unshakable response to the growing power demands created by our ever-changing technology world, influencing both our present and the electrified future.

Each installment in this article series serves as a comprehensive resource, imparting precise guidance and providing aid to the design and application engineers with the required insights to construct a smarter, more dependable, and cost-effective solution based on the sophisticated specification provided by the OCP ORV3 BBU. This is accomplished by providing a meticulously part selection process, prepared guidelines, engineering methodologies, and procedural recommendations.

References

1 David Sun. “Open Compute Project Open Rack V3 48 BBU Rev: 1.3.” Open Compute Project, November 2022.

Authors

Christian Cruz

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 than 12 years of engineering experience in the field of analog and digital design, firmware design, and power electronics, which includes power management IC development as well as AC-to-DC and DC-to-DC power conversion. He joined ADI in 2020 and is currently supporting power management requirements for cloud-based computing and system communications applications.

Ralph Clarenz Matocinos

Ralph Clarenz Matociños

Ralph Clarenz Matociños graduated with a bachelor’s degree in electronics engineering from Pamantasan ng Lungsod ng Maynila (PLM) in Manila, Philippines. He has over a year of engineering experience in power electronics, including battery management system development and DC-to-DC power conversion. He joined ADI in 2022 and currently works as a power systems applications engineer for cloud and data center applications.