Ultralow Noise Switching Power Supplies for Reduced Electromagnetic Interference

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07 Nov, 2022

Ultralow Noise Switching Power Supplies for Reduced Electromagnetic Interference

Article #2 of Power Management for Tomorrow’s Innovations Series: Electromagnetic Interference is a noise originating from fast switching electronics that affects circuits in close proximity. Innovations in silent switching can significantly reduce its effects without the addition of a dedicated filter circuit.

This is the second article in an 8-part series featuring articles on Power Management for Tomorrow’s Innovations. The series focuses on power management and optimization techniques for modern electronic systems. This series is sponsored by Mouser Electronics. Through the sponsorship, Mouser Electronics shares its passion for technologies that enable smarter and connected applications.

Many electronic products must pass Electromagnetic Interference (EMI) compliance tests—such as the Federal Communications Commission (FCC) Part 15 rules in the United States (US)—before being released into the market. When a company’s product fails EMI compliance tests, the company loses control of the development process. Shipping dates begin to slip, projected revenues diminish, and expenses start piling up. These tests are critical because excessive noise can interfere with nearby electronic devices and sensitive electronic components within the product itself. 

In this article, we introduce our readers to silent switching and some application circuits by Analog Devices that can be used to reduce EMI issues in electronic products—more specifically, in switching power supplies.

The Root Cause of EMI issues

Often the EMI compliance problem lies in the product’s switching power supply. Electronic products must be designed from the beginning with EMI compatibility in mind. In these cases, the proper solution is to prevent it by using an ultralow noise-switching power supply in the initial design, rather than adding shields and filters to the product later. 

A Case Study of Silent Switcher Technology

A Silent Switcher device breaks the trade-off between EMI and efficiency by not needing to slow down the switch edge rates.  To understand how the technology works, let’s consider the example of the LT8614 Synchronous Step-Down Silent Switcher and compare it with a regular LT8610 High-Voltage Buck Regulator (Fig. 1). Both the Integrated Circuits (ICs) are made by Analog Devices and are available from Mouser Electronics. LT8610  is a 42V input-capable, monolithic (with Field Effect Transistors inside) synchronous buck converter that can deliver up to 2.5A output current. Notice that it has a single input pin (VIN) at its top left corner.

Fig. 1: How to turn an LT8610 into a Silent Switcher device—the LT8614. Source: Analog Devices

However, when contrasting the LT8610 with the LT8614 (a 42V input-capable, monolithic synchronous buck converter that can deliver up to 4A of output current), one can see that the LT8614 has two VIN pins and two ground pins on the opposite side of the package. This is significant since it is part of what makes it silent switching.

Making a Switcher Silent

Placing two input capacitors on opposite sides of the chip between the VIN and ground pins will cancel the magnetic fields. The figure highlights this with red arrows pointing to the capacitor placement on the schematic and the demo board as shown in fig.2.

Fig. 2: Diagram of the LT8614 showing the filter caps between VIN and ground pins on opposing sides of the Integrated Circuit (IC). Source: Analog Devices

Highly Efficient Operation Even at High Switching Frequencies

Silent Switchingoffers high efficiency at high switching frequencies (>2MHz) with ultralow EMI emissions, offering very compact solutions while optimizing high efficiency at light load with ultralow quiescent current (IQ). The Silent Switcher family devices use unique design and packaging techniques to offer 95% efficiency at 2MHz while effortlessly passing the Comité International Spécial des Perturbations Radioélectriques (CISPR) 25 Class 5 Peak EMI limits.

Eliminating PCB Layout Sensitivity

The Silent Switcher 2 Regulators have exceptional EMI/EMC performance, and a small overall solution size to eliminate Printed Circuit Board (PCB) layout sensitivity (Fig. 3). The Silent Switcher 2 Regulator series features allow these devices to get employed on any PCB, simplify product design, and reduce risks even when using two-layer PCBs (Fig. 4).

Fig. 3: Silent Switcher devices split the hot loop into two power loops with mutually canceling magnetic fields. Silent Switcher 2 devices integrate the hot loop and warm loop caps into the package to simplify the board layout. Source: Analog Devices

Fig. 4: Silent Switcher devices, such as the LT8640 Step-Down Regulator, confine the magnetic field, producing a lower EMI part. Source: Analog Devices

Silent Switcher® Architecture by Analog Devices for Building Ultralow Noise Switching Power Supplies

To overcome these challenges, Analog Devices offers Silent Switcher® Architecture which minimizes the risk of problems caused by EMI, making µModule Power Modules, Regulators, and Discrete DC-DC ideal for noise-sensitive applications. These power products support functions like a Step-Down (Buck), Step-Up (Boost), Step-Down and Step-Up (Buck-Boost), Battery Charger, Isolated Converter, and LED driver.

A synchronous buck converter produces a regulated voltage lower than its input voltage. It enables designers to deliver high currents while minimizing power loss. Analog Devices Inc. LTC3310S Synchronous Step-Down Silent Switcher® 2 DC-DC Converter achieves low EMI and high efficiency at switching frequencies as high as 5MHz. The device can provide up to 10A output current from a 2.25V to 5.5V input supply in a compact 3mm x 3mm LQFN package. It’s ideal for automotive applications, servers, telecom power supplies, and more. LTC3310S also includes a power good signal when the output is in regulation, output overvoltage protection, thermal shutdown, a temperature monitor, clock synchronization, mode selection, and output short circuit protection.

Conclusion

Power supplies are the primary sources of EMI that create distortions in nearby electronic devices if not managed properly. Filters are often used to eliminate such issues but better approaches are available in the market. 

Silent Switchers are smaller, and cost-effective alternatives to filters that reduce EMI right where it is produced. The technology makes it easier for switch mode power supply designs to pass the various noise immunity standards such as CISPR 32 and CISPR 25. 

This article is based on an e-book by Mouser and Analog Devices. It has been substantially edited by the Wevolver team and Electrical Engineer Ravi Y Rao. It's the second article from the Power Management for Tomorrow’s Innovations Series. Future articles will introduce readers to some more power management and optimization techniques for modern electronic systems.


The introductory article covered the fundamentals of power electronics, the technology behind highly-efficient power conversion in different electrical/electronic systems. 

The first article shares some design techniques for efficient power management in EVs. It covers how manufacturers can build significantly better vehicular electric power systems with systematic planning and innovative power electronic solutions.

The second article introduced readers to silent switching and how it prevents EMI at the source, rather than adding shields and filters to the product later. 

The third article describes current measurement techniques using LTC297x series components by Analog Devices. It presents some application circuits and compares different approaches for current sensing in power electronic converters. 

The fourth article discussed the problems associated with phase noise and experimentally showcased how power supply designs can be optimized to deal with them.

The fifth article featured Single-Inductor Multiple-Output architecture that integrates different power supply functionalities to drastically reduce the overall size and costs for wearables.  


About the sponsor: Mouser Electronics

Mouser Electronics is a worldwide leading authorized distributor of semiconductors and electronic components for over 1,100 manufacturer brands. They specialize in the rapid introduction of new products and technologies for design engineers and buyers. Their extensive product offering includes semiconductors, interconnects, passives, and electromechanical components.

References

[1] Yingyi Yan, Eugene Cheung, Eric Gu, and Tuan Nguyen, ‘See Industry’s First Dual 70 A SilentMOS and Single 140 A Smart Power Stage’, Analog Devices, [Online], Available from: https://www.analog.com/en/design-notes/see-industrys-first-dual-70-a-silentmos.html

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Mouser Electronics is a worldwide leading authorized distributor of semiconductors and electronic components.

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