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Power Developer October

Designing for

Durability

2013

Power Developer

4 10 16

CONTENTS

TECH COLUMN

How to GaN: eGaN FETs in Hard Switching Bus Converters

TECH ARTICLE

DC/DC Converters as Isolation Barriers in Inverters

LEAD INTERVIEW

Peter Kaczmarek - President & CEO of Astrodyne

FEATURED ARTICLE

TECH ARTICLE

Cymbet’s Solid-State Battery

Capacitor Voltage Ratings in VCORE Applications

PRODUCT HIGHLIGHT

Power Integrations’ Qspeed Diodes

Power Developer

TECH ARTICLES

Alex Lidow

CEO of Efficient Power Conversion (EPC)

Power Developer Click below to read last month’s column:

In the previous column of this series, some of the design considerations for the traditional buck converter were presented. In this installment, more complex hard switching converters used for isolated DC to DC power conversion will be discussed. The isolated DC to DC bus converter is widely used in computing and telecommunication systems as part of the intermediate bus architecture (IBA) approach. It is available in a variety of standard sizes, input and output voltage ranges, and topologies as shown in figure 1. Their modularity, power density, reliability, and versatility has simplified and to some extent commoditized the isolated power supply market. As these “brick” converters are of strictly defined sizes, designers are forever coming up with innovative ideas to increase their output power (and power density). Although these ideas are numerous and varied, they are all related to system efficiency, as the maximum power loss for a given standard size is fixed based on the surface area of the converter and method of heat extraction.

Consider an eighth brick converter as an example – although there are numerous input and output voltage configurations, topologies and output range tolerances (regulated, semiregulated, and unregulated), they all have very similar maximum power loss numbers at full power (i.e. between 12-14 W). This is a physical limit based on the fixed surface area of the converter and the method of heat extraction. Thus, for an eighth brick converter that is 93% efficient at full load, the maximum output power (assuming 14 W loss) will be about 186 W. If the efficiency can be improved by just 1%, the output power would increase to 220 W. That’s an 18% increase in output power!

Hard Switching Intermediate Bus Converters The majority of today’s bus converters use traditional hard switching bridge topologies operating at a low frequency range (150 kHz to 250kHz) to maximize efficiency. At these lower switching frequencies, the isolation transformer and output inductor are very bulky, occupying a large portion of the board area. To improve their power density, the operating frequency must be increased to be able to process more power through the inductor and transformer. As switching frequency increases, however, the losses from MOSFET body diode conduction, reverse recovery, and switching increase significantly, limiting the converters output power capability. Because of this, power density improvements have come from changes in design optimization and topology changes with actual switching frequencies decreasing, rather than increasing.

Eighth Brick Converter with eGaN FETs

Figure 1: Intermediate bus architecture (IBA) showing voltage ranges for bus converters.

To showcase the improvements that eGaN FETs offer in this design space, a high switching frequency eGaN FET based eighth brick bus converter was constructed. For the eighth brick converter, we chose a full-bridge primary side converter with a full-bridge synchronous rectifier as shown in Figure 2. This demonstrates the ability to use a large number of eGaN FETs and drivers within the limited eighth-brick footprint. The actual converter is shown in Figure 3 and compared side by side to a similar MOSFET-based converter. To the skilled designer, the significant amount of ‘green’ space (unfilled PCB area) could be further exploited to improve efficiency.

TECH ARTICLES

Figure 2: 200 W 1/8th brick fully regulated, full-bridge primary with full-bridge synchronous rectification using eGaN FETs

Figure 3: Comparison between the 48 V to 12 V eGaN FET-based eighth brick converter (lower image) and comparable silicon based converter (upper image) showing top and bottom views (scale in inches).

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Figure 4: Efficiency comparison between an eGaN FET and MOSFET based eighth brick converter.

Since the initial eGaN FET based brick comparison, the topological developments of brick converters has continued to squeeze more performance out of MOSFET based systems. In Figure 5 the output power of three different generations of regulator eighth brick converters are plotted versus their switching frequency. What is clear from this figure is the continuing downward trend in switching frequency as well as in increase in overall converter loss (given in brackets below each point). This overall increased converter loss puts additional strain on the thermal design of these converters, which require complex thermal derating curves. Although the reduction in switching frequency is instrumental to increasing the converter power output, increases the allowable power loss budget is also significant. For the same increase in power loss budget as between generations 1 and 3 of the MOSFET based converters, the eGaN FET based converter shows a potential 35% increase power output to 250 W (green circle in Figure 5) without a decrease in frequency. Based on figure of merit advantages and comparisons of many different topologies, it is assured the eGaN FETs will outperform MOSFETs in each and every hard switching intermediate bus converter.

Summary

Figure 5: Switching frequency vs. rated output power for different generation MOSFET based eighth brick converters with comparison to eGaN FET based converter (losses at rated power given in brackets).

In this column we presented an eGaN FET based isolated brick converter and compared it against similar MOSFET based designs. Due to the limitations of silicon MOSFETs, designers have squeezed more power out of the thermally constrained brick converters by reducing the switching frequency. With eGaN FETs, offering lower figures of merit and reduced switching losses, future increases in both efficiency and power output can be achieved for isolated brick converters operating at frequencies beyond the capability of aging Si MOSFETs.

Experimental Results

eGaN is a registered trademark of Efficient Power Conversion Corporation. â&#x2013;

Efficiency results of the eGaN FET based converter compared to the same MOSFET based brick converter are shown in Figure 4. Despite the eGaN FET converter operating at 33% higher frequency, it is able to produce 15% more output power for the same power loss. As the eGaN FET based converter has not been optimized in either topology, thermal design or switching frequency, further improvement should be possible.

TECH ARTICLES

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Power Developer

Like a Levee

in a F

DC/DC converters as

TECH ARTICLES

Flood

s Isolation Barriers in Inverters

You can’t feed electricity from a solar power plant or wind turbine straight into the mains—you have to convert it using an inverter. IGBTs are fast power switches that “float” on high potentials and need to be galvanically isolated from the control electronics. Like a levee that keeps the flooding away from the land behind it, highly isolated DC/DC converters make sure that your installations are kept shored up against “flooding” before time.

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ukushima speeded up the transition to regenerative energies, at least in Germany, but unfortunately, neither the wind nor the sun provide us with electrical power the way we need it. The sun doesn’t shine all the time, and then only ever by day; the wind also blows at night, but you can’t schedule industry according to the Beaufort scale. Apart from that, offshore wind farms are far from the places needing their energy. This calls for new ways of transporting and storing energy, but that’s only one side of the coin – the other is getting wind and solar into the mains at the right voltage, frequency and phase. That involves a lot of serious engineering. Turning solar and wind power into mains power Wind turbine generators already produce AC, but the problem is that you can’t synchronise them to the mains in frequency or voltage even with variable turbine blades. The same applies to solar systems – the voltage in the collectors falls towards zero by the time the sun sets behind the horizon at the latest, let alone the fact that solar cells generate DC anyway. This means

processing electrical energy generated by two completely different systems in a way that you can feed into the grid while keeping losses to a minimum. As a general rule, this takes two steps – the first turns the energy input into high direct current, and the second converts the DC into the AC required for the grid. Fig. 1 shows a solar system as a block diagram. The boost converter (left half) turns variable voltage from a solar cell depending on solar intensity into constant, high-voltage direct current. This is where an IGBT or isolated gate bipolar transistor controlled by a pulse width modulation signal comes into the picture. The duty cycle is regulated in such a way as to ensure the required direct current on the capacitor upstream from the rectifier. Two IGBT pairs serving the inverter (right half) are controlled opposite inphase from a PWM signal working at a frequency of at least 10kHz. The duty cycle varies inn a 50Hz rhythm to ensure a sine-wave voltage of 230V/50Hz in phase synchronisation with the mains supply voltage.

Figure 1: Function diagram of a solar plant with a booster (left) and inverter (right). The IGBT drivers need effective galvanic isolation from the low-voltage side using high-isolation DC/DC converters.

TECH ARTICLES IGBT – A Secret Weapon in HighPower Electronics? In technical terms, IGBTs are a hybrid affair, acting as MOSFETs on the input side and as bipolar transistors in the collector-emitter loop. They need virtually no current to control, at least in relation to the electrical currents they themselves switch. In the ON state, they show the low voltage drop typical for bipolar transistors on the collectoremitter loop, which makes them ideal for switching high voltages and currents while keeping losses relatively low – no surprise that they’ve become the be-all and end-all in inverters and boost converters. Controlling IGBTs is anything but trivial. The control electronics and processor operate at low voltage, and are physically grounded. The individual inverter IGBTs, on the other hand, “float” at different potentials to each other and to ground, so both need effective galvanic isolation from one another. Optoisolators would easily solve the problem if it weren’t for a few additional aspects that need attending to – IGBTs need a positive voltage to switch on and a negative voltage for rapidly discharging gate capacitance while switching off. The switching edges provided by control electronics are not nearly steep enough to ensure efficient IGBT switching, and IGBTs that claim to be controllable at zero power actually need more power than the processor or optoisolator can provide, so extra drivers need to be installed between the IGBT and the other components.

Need for Galvanic Isolation Using DC/DC Converters The drivers speed up the switching edges to 1000V/μs or more, generating the current needed for charging the IGBT’s input capacitance. The driver itself needs a voltage supply of +15V. Switching off requires fast gate capacitance discharge, which is taken care of by applying negative voltage – -9V has proven to be good in practice. DC/DC converters with proper galvanic isolation supply both voltages. Isolation might not seem to be too much of an issue at moderate voltages such as 600V – relatively simple transformers with enamelcoated wires for insulation and overlapping

= IGBT PWM Signal (10kHz) = Smoothed Output Voltage Figure 2: Two IGBT pairs in simple inverters are controlled using a PWM signal at high frequency opposite in-phase to ensure a sine wave at the output in synchronisation with the mains supply voltage.

windings are more than enough for voltages of 1kV and more. However, you will have to take a much closer look at it if you want long service life from your system – this is a complex area. For example, the insulation resistance of DC/DC converters is generally specified at 50Hz, whereas IGBT circuits usually work at frequencies in excess of 10kHz due to the increased efficiency. We don’t fully know how electromagnetic components work at that frequency, so you will need to allow a margin of safety in your calculations. You will also have to remember that the circuit works at very steep edges to minimize losses, but the high dV/dt at 1000V/μs and more has effects elsewhere – steep edges running into parasitic capacitances that you will find around the IGBT and converter transformer will lead to heavy spiking at amplitudes that you cannot plan for in any calculation. Your instrumentation will not give you any reliable results either – the oscilloscope’s probe will give you lower spike readings across the board than are actually occurring in reality. Effects such as these place a constant burden on DC/DC converters; exceeding the specified limits will not usually damage your DC/DC converter, but this long-term punishment will wear out the insulation the same way that a levee might remain intact for years before breaking after being softened up by long periods of flooding. There are no guarantees here since you have no way of accurately assessing the limit values. Inverters have a long service life while maintenance and outages are expensive, so it always makes sense to keep on the safe side in selecting a suitable converter – such as when you opt for DC/DC converters that can withstand the anticipated spikes in constant operation.

Power Developer

A Useful Tool for Comparison Data It’s not difficult to work out why the limit for isolation in constant operation is much lower than short-lived spikes. There is no general rule for this situation, but we at RECOM provide users with very helpful comparison data on a disc the size of a CD to give you the corresponding comparison values for every reference value. As an example, if you select the one-second 4,000V DC test voltage as specified for a RECOM RK-0515S as in Fig. 3, you will see the permitted limit values for one minute or constant operation at 3,200V DC and 1,800V DC, respectively, on the right. In plain terms, that means that a DC/DC converter specified at 4,000V DC can only handle up to 1,800V DC in constant operation; you should always include the difference as a safety margin in your calculations to make sure that you’re protected against electrical and mechanical challenges in the future. Due to the low costs involved, many users even opt for converters with more effective insulation, especially as this does not affect the design and size of the converter due to new transformer technology. You can try out our convenient Isolation Calculator at our website, www. recom-electronic.com and order it from info@ recom-electronic.com free of charge.

Figure 3: RECOMS’s decider disc gives you the comparison data you need for any isolation specification, the RK-0515S specified for 4,000V DC shown here as an example.

Figure 4: RECOM’s new converter generation has dual asymmetric outputs with output voltages of +15V and -9V as needed for IGBT applications.

Broad Product Range for IGBT Applications Each driver has needed two DC/DC converters each up to now for IGBTs and their asymmetric power supply with positive and negative voltage mostly at +15V and -9V. Successful examples from the RECOM range include the RK-xx09S/RK-xx15S (1W) converter pair and a test voltage of 4,000V DC/1s or the RPxx09S/RP-xx15S (1W) converter pair at 5,200V DC/1s, although the RxxP09S/RxxP15S (1W) and RxxP209S/RxxP215S (2W) converter pairs at 6,400V DC/1s test voltage give you even more effective isolation. All of our models come in compact SIP7 casings and use natural cooling at ambient temperatures of up to 85°C without derating. May 2013 saw a new converter generation with dual outputs launched onto the market; the four product ranges are available with the same isolation voltages as the above converter pairs, but both generate the +15V and -9V voltages necessary for IGBT applications – you will only one DC/DC converter for each driver in the future. All models are available with selectable 5V, 12V, and 24V input, are certified according to EN-60950-1 and EN60601-1, and are also completely lead-free according to RoHS 6/6. They come with a three-year guarantee. ●

TECH ARTICLES

All the forces in the world are not as powerful as an idea whose time has come. —Victor Hugo, 1800

Power Developer contains new ideas that come every month. —Power Developer Editors, 2013

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Power Developer

Designing for Durabi Peter Kaczmarek,

President and CEO at Astrodyne Corporation

Astrodyne is a global developer of advanced power conversion parts for high intensity applications. The company specializes in unique switching power supplies and converters geared towards a variety of challenging industries from Aerospace and Defense to Medical and Industrial. Although a relatively small company, Astrodyne has made some major acquisitions over the years that allow them to truly differentiate their power products from their competitorâ&#x20AC;&#x2122;s. Peter Kaczmarek, the CEO of Astrodyne, came to the company last year because he saw an opportunity to help grow a company with already great legacies, products, and marketing divisions. Power Developer got the chance to talk with Kaczmarek about his growth strategy for the company, some of the unique product families they have acquired, and the new industry segments the company plans on expanding into.a smaller layout footprint on the PCB for the regulator overall.

COVER INTERVIEW

ility

Power Developer

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We can uniquely design a product for a particular application, but also provide standard solutions when it is best for the customer. We have a balanced approach that a lot of other companies don’t have. How would you sum up the breadth of Astrodyne’s products? Astrodyne is a very unique company in the power supply industry. As you know, it’s a pretty crowded industry with some large companies and a whole lot of smaller ones. Astrodyne is a company that would probably be considered medium-size in that universe, but we have some great technologies that we can bring to bear for demanding power applications. For example, a couple of years ago, we acquired a company called Jerome Industries in New Jersey. Their claim to fame is medical power supplies that achieve ultra low leakage current requirements required, for example, in applications where a patient in a might come in contact with the powered device. Infusion pumps, ventilators, oxygen concentrators, electrosurgery equipment, and monitoring devices all fall into that category. That’s a pretty tough standard to meet and our Jerome brand products meet the needs easily. We’ve also acquired the product lines of another company called RO Associates, in Fremont, California. Their claim to fame is very high power density, small format, power components which are used in very harsh environment applications with very high temperature swings, shock and vibration. Examples include aircraft cabin electronics, aircraft galleys, in-flight entertainment avionics, satellite communications and weapon guidance systems. As you can see, Astrodyne is a company that has a wide variety of standard products and solutions, but also some really unique products and technologies that you can’t find anywhere else.

It seems like you sell power products at the component level and you have some products that are more of a solution than a component. What percent of your business would you say is component sales and what percent is modules and solutions? That’s a great question and is difficult to answer. Our customers are faced with a wide array of power challenges and we assist with standard products, custom solutions or technical advice as the issue warrants. Today, a vast majority of our sales would be an entire power solution, whether it’s an external or an internal power supply. A smaller, but fast-growing part is at the component level, especially with high performance products. I should also add that Astrodyne develops and manufactures about 75% of what we sell. The other 25% is sourced through industry partnerships that we’ve had for almost two decades. Our goal is to add value with our technical expertise and superior service levels. At times that solution may include products from partners with whom we work closely. We can uniquely design a product for a particular application, but also provide standard solutions when it is best for the customer. We have a balanced approach that a lot of other companies don’t have.

If there are clients that plan on integrating one of your products in a large production environment, are you able to work with clients that way? Our niche would be what I would call high complexity, small-to-medium volume applications. We have a wholly owned, full-

COVER INTERVIEW service manufacturing facility in Shanghai, China, as well as a full-service manufacturing facility in Elizabeth, New Jersey. Both are ISO-9000 and ISO-13485 certified by UL, and utilize a common quality assurance system. With those facilities, we can scale our manufacturing capabilities as required to meet our customer needs. We have found that customers with demanding power conversion requirements are often those that may have lower volume, higher mix and long horizons, so we have optimized our facilities to meet those needs. We can also flexibly serve a customer who wants US-made products or wants them sourced in Asia. Some customers want us to both at the same time, and our complementary factories allow us to do that easily.

As a company, are there any particular industries that you are focused on growing or expanding into? Absolutely. The biggest change that we’ve made since I’ve joined is to focus on the markets and applications where we really feel that we offer a differential advantage for customers. We are primarily focused on three markets: medical devices, defense and aerospace, and niche industrial applications. Within each of those three markets, we’ve identified six to eight application spaces where we believe we can offer a real advantage in the industry.

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The biggest change that we’ve made since I’ve joined is to focus on the markets and applications where we really feel that we offer a differential advantage for customers.

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One example would be in the medical market, with circulatory devices designed to assist a patient’s ailing heart. We have an industry-leading position in providing the power solution to the companies that are making these amazing heart-assist devices. You can imagine that it’s a very tricky, very demanding application that requires specific certifications and safeguards. Our products are uniquely suited to that need, based on our ultra-low leakage current magnetics design, experience with reliable mechanical configurations and credibility in the industry. It is a real comfort to a new customer in an application like this one to find a power supply partner that already knows what is important to the customer and the patient. We’ve focused on a number of application spaces like that one, and we’re proactively going to the customers in those spaces and presenting our solutions. We are finding a really receptive audience.

Power Developer

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The first thing that struck me about the people at Astrodyne is that they are extremely customer-focused. If the customer needs something, we’ll turn the company upside down to make it happen.

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In one of your comments earlier, you said that part of your plan has been acquisitions. Do you anticipate that acquisitions will continue to be part of the growth strategy at Astrodyne? There is no question about that. We are majority owned by the Audax Group, a private equity firm out of Boston that focuses on successful middle market companies and partners with their management team to drive growth. They’ve owned us since 2008 and have provided the capital to invest in both organic growth and acquisitions. As I’ve said, we’ve made two acquisitions since they’ve owned us and we continue to be extremely active in looking - for not just any acquisition, but one where there is some unique technology that we can bring to customers in our markets of interest.

Are there any products that have been really popular among your customers? There are really good examples of exciting new products in each of our product families. A new product in our RO family of AC-to-DC products is the PFC-375. This product is already available to key customers, and it is receiving great acceptance for its extremely high power density and very small footprint. Like our other RO products, it has tremendous thermal properties, so it can handle a wide variety of temperature

COVER INTERVIEW ranges and environmental conditions, as well as a wide range of input voltages and frequencies. A lot of defense, aerospace, industrial and medical customers are really excited about the PFC-375. In the Astrodyne product family, we have a wide family of real workhorse products. We are particularly well known for our products in the 10- to 300-watt range. There are numerous families including medically approved versions that are extraordinarily reliable and can be used in a very broad range of applications. A great new example is our PMMX-300S-E series. It is a medically-rated power supply with a very compact design and active power factor correction. We have launched this family with output DC voltages of 12 through 48 volts. We work very closely with our customers to use products like these in applications where they can get the maximum amount of power in the smallest footprint, along with extremely high MTBF and consistent performance. In the Jerome Industries family, our products specialize in ultra low leakage power supplies for medical applications where there is patient and/or operator contact. Jerome’s real expertise is that they can take a basic footprint of what you need in terms of power and form factor and quickly tailor it to a specific application—input/output options, and many other variations. A great new example is our PSX300 series. It is a medically-rated product available with a wide range of output voltages, 260 watts of output power, Class I and II input options and extremely low leakage current. For a compact product, it has very high power density but also runs very cool and quiet, important for many medical applications.

How would you describe the culture at Astrodyne? Thanks for asking! The first thing that struck me about the people at Astrodyne is that they are extremely customer-focused. If the customer needs something, we’ll turn the company upside down to make it happen. I’ve found everyone to be open to new ideas and interested in the devices that our products power. On top of that, we have some incredible breadth and depth of power supply experience. For example, we recently held an open house to mark the 50th anniversary of RO Associates, which was started by one of the true pioneers of the power supply industry, Dr. Robert Okada. The Jerome

Industries business turns 50 years old next year! Besides that, many of our engineers count their industry experience in the decades. It is great to be in a company that acts young and flexible, but with extensive wisdom and technical experience. Through the acquisitions and industry expertise that we’ve gathered, we have people who really know their stuff. Combining that knowledge with that customer focus and desire to please and solve a problem is a really powerful combination. When I joined Astrodyne and took a look at our website and started asking people in the industry what they knew about the company. I found that a lot of people still thought the company was primarily a distributor, which was a historical strength. However, we’ve changed a lot. Today the vast majority of our business is from products designed and manufactured internally. So, in order to make that clear to the marketplace, we’ve recently completely overhauled our website and updated our brand image through promotion to ensure that people understand that Astrodyne is really a global developer and manufacturer of solutions. We do still, as I said earlier, offer products that we source from partners, but our primary strength is designing and building power solutions for demanding applications, particularly for medical, military, and industrial devices. I encourage people who haven’t checked Astrodyne out recently to check our website and realize that we are a full-service manufacturer with two world class manufacturing facilities and three world class design centers worldwide. Please let us know how we are doing! In closing, I want to bring to your attention our new company tagline: Now you have power. I love it because it has many possible meanings, all of them important. For our employees, it means they’ve found the power of a supportive team and work environment in which to serve customers and further their career. To our suppliers and industry partners, it means they have the power of a global partner with a strong pedigree, solid commercial network, and exciting future. Most importantly, to our customers, it means that with Astrodyne, they’ve not only found the exact power solution they need, but also an ongoing partner and technical expert to work to assist them in their newest challenges. Now you have power! Astrodyne Corporation is a really exciting place to be. ■

Power Developer

Solid-State Batteries The Embedded Advantage

Steve Grady talks about Cymbetâ&#x20AC;&#x2122;s competitive advantage with solid-state batteries and the move towards true system-inpackage devices.

FEATURED ARTICLE

devices. Cymbet not only makes extremely small lithium solid-state batteries, it can also make them in unique shapes. Because Cymbet uses semiconductor-style techniques to create the batteries, they can make big or small batteries, and odd-shaped batteries. Using patented laser ablation techniques to separate the bare die batteries allows for the potential to create 3D batteries—if the devices were stacked in interesting shapes. This gives customers a lot of flexibility, Grady said. “One of the key advantages of solid state battery technology is that you can carve out whatever shaped energy storage device you want—that's a capability that's really never been available to designers before.” This flexibility, along with the fact that batteries are highly reliable and designed to last the life of a product, contributes to one of the most interesting advantages of solid-state batteries. This advantage is the close integration that can be achieved in a product with a solid state battery. Because EnerChips are attached, assembled, and treated like every other device on a board, there are no special assembly issues, transportation issues, and they last the life of the product. “What that means,” said Grady,

“is that we're seeing product designs where there are no doors or openings. Customers can't get into the products—they're essentially sealed.” This design aesthetic is everywhere now, Grady pointed out, because the lack of user access to a product allows the reliability of that product to go way up. “You're not going to get water, you're not going to get dust,” said Grady, “you won't have somebody break the door—not going to take out the battery and do things to the inside. Having sealed products improves your warranty and return costs, and we're seeing a lot of customers loving these rechargeable batteries that are buried in the product. They allow the creation of product configurations that are much more reliable.” With EnerChips, Cymbet hopes to capitalize on a market trend of smaller and smaller electronics, and higher and higher integration. These miniature devices need power, and because the EnerChip is essentially a battery IC, and is constructed just like the ICs it's co-packaged with, the EnerChip can be packaged side-by-side, or stacked on top of other devices using 3D packaging techniques. According to Grady, this allows customers to “truly have a system-in-package kind of device and provides a key competitive advantage.”

Power Developer

Capacitor Voltage Ratings in

VC OR E

TECH ARTICLES

Applications— Is Bigger Necessarily Better? Carmen Parisi—Intersil Applications Engineer With laptops continuing to slim down in form factor and tablets grabbing larger market shares as time goes on available PCB space is vanishing quickly. To fit into smaller PCB areas, power electronics designers are forced to rely on higher switching frequencies for their DC-DC converters in order to reduce the size of the solution. The largest contributors to the solution size are typically the output filter composed of an inductor and a few capacitors. Traditionally, the output capacitance is realized as a combination of bulk capacitors, e.g. OScaps, tantalums, and electrolytics, as well as multi-layer ceramic capacitors (MLCCs) sized to meet both steady state ripple requirements and transient over- and under-shoot specifications. The push to higher switching frequencies however limits the performance of the bulk capacitors in applications with strict performance requirements such as Intel’s VR12.6 specification since ESR and ESL parasitics can no longer be neglected. Because of this a greater number of VCORE applications are adopting an all ceramic solution for their output capacitance. Switching to all ceramic capacitors allows for both a lower BOM cost as well as a smaller layout footprint on the PCB for the regulator overall.

Power Developer O

ne issue when designing an all ceramic solution is whether one ceramic cap is as good as another. For example, does a prototype built with capacitors on hand rated for 16V mimic the performance of production boards populated with 6.3V ceramics? How does the performance of one capacitor compare against a similar capacitor from another vendor? Like many aspects of circuit design, a definite answer is neigh impossible to give and there many shades of gray. To review the performance of five different ceramic capacitors with respect to load transient overshoot, designers tested using the ISL95813 – Intersil’s new single phase buck regulator designed to meet the Intel VR12.6 specification. All five capacitors were 22µF, 0805, X5R MLCCs, a popular choice in many VCORE applications, and came from three different vendors. A 6.3V and 16V capacitor was chosen from one product

line from each of two vendors A and B to evaluate the effect of voltage rating on performance. Vendor C did not make a 16V, 0805 capacitor and so a 6.3V rated one was chosen. The ISL95813 evaluation board was configured for a 2-cell application to meet the 15W VR12.6 specification which has ICCMax = 32A and maximum PS0 transient of 27A. As defined by Intel, the AC overshoot loadline is equal to 9.4mΩ allowing for a maximum overshoot of 253.8mV upon load release. To meet the necessary application requirements the 15W ISL95813 design has a 700kHz switching frequency; an output LC filter composed of a 150nH, 0.9mΩ inductor; and 14×22µF MLCCs on the output. For the full 15W reference design please see Figure A in the Appendix.

Applications—

s Bigger Necessarily Better? Carmen Parisi—Intersil Applications Engineer With laptops continuing to slim down in form factor and tablets grabbing larger market Figureon 1: Vendor A 27APCB Singlespace Step Transient Overshootquickly. Left) 6.3V To MLCCs (207mV) Right) 16V shares as time goes available is vanishing fit into smaller PCB areMLCCs (226mV) as, power electronics designers are forced to rely on higher switching frequencies for their DC-DC converters in order to reduce the size of the solution. The largest contributors to the solution size are typically the output filter composed of an inductor and a few capacitors. Traditionally, the output capacitance is realized as a combination of bulk capacitors, e.g. OScaps, tantalums, and electrolytics, as well as multi-layer ceramic capacitors (MLCCs) sized to meet both steady state ripple requirements and transient over- and under-shoot specifications. The push to higher switching frequencies however limits the performance of the bulk capacitors in applications with strict performance requirements such as Intel’s VR12.6 specification since ESR and ESL parasitics can no longer be neglected. Because of this a greater number of VCORE applications are adopting an all ceramic solution for their output capacitance. Switching to all ceramic capacitors allows for both a lower BOM cost as well as a smaller layout footprint on the PCB for the regulator overall. Figure 2: Vendor B 27A Single Step Transient Overshoot Left) 6.3V MLCCs (258mV) Right) 16V MLCCs (203mV)

TECH ARTICLES

Figure 3: Vendor C 27A Single Step Transient Overshoot, 6.3V MLCCs (223mV)

The performance of the 6.3V and 16V capacitors from Vendor A showed 14 capacitors were sufficient to meet the overshoot specification set by Intel. The capacitors rated for only 6.3V showed nearly 20mV less of single step overshoot as compared to their higherrated counterparts. Sweeping the load frequency up to 1MHz as specified in Intelâ&#x20AC;&#x2122;s test documentation showed that the overshoot never exceeded the 253.8mV allowed with either of the two different MLCCs on the eval board. Further checks of the CCM and DCM ripple showed that 14 output capacitors were enough to meet the rest of the 12.6 specifications with either voltage rating. By taking specific care during layout when using Vendor Aâ&#x20AC;&#x2122;s 6.3V capacitors, it may be possible to knock off one or two output capacitors, depending on how much margin is desired when meeting the overshoot specification. As the amount of output capacitance is reduced, the ripple on the output voltage increases, so a balance must be met between the overshoot, ripple, and BOM cost design goals to ensure the adequacy of all performance aspects.

Outfitting the eval board with capacitors from Vendor B also showed a significant performance difference between the 6.3V and 16V capacitors. With 6.3V capacitors in place the design exceed the allowable overshoot by approximately 4mV in the single step case. Sweeping the load to 1MHz increased the overshoot at higher frequencies further invalidating the design. Though the rest of the 12.6 requirements were met with 14 capacitors, two more were needed to allow for sufficient margin on the repetitive load transient bringing the total number of output capacitors up to 16. The 16V capacitors from Vendor B met the overshoot specification with nearly 50mV of margin across the entire load step frequency range. Testing the other areas of the 12.6 spec indicated that once again, 14 capacitors were sufficient for this design. As before, in applications where space constraints are the limiting factor on a design it may be possible, with proper layout, to remove one or two of the output capacitors and still meet spec but care would need to be taken not to exceed the steady state ripple limits.

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Figure 4: ISL95813 – 15W, VR.12.6 Reference Design

While Vendor C does not make a 16V MLCC in a 0805 package their 6.3V caps proved more than adequate when testing the ISL95813. Their 6.3V caps met the repetitive load test with roughly 30mV of margin over the full range of tested frequencies. Keeping the 14 capacitors on the output as called out by the reference design met the 12.6 specification satisfactorily. Table 1 above summarizes the results collected during this experiment and gives the associated BOM costs with each output capacitor option. While typically offering comparable performance to the 6.3V capacitors, the additional cost associated with the 16V rating makes them prohibitively expensive for low voltage VCORE applications.

When comparing the 6.3V capacitors it’s clear that a higher cost does not always equal better performance as evidenced by needing an additional two capacitors when placing the components from Vendor B on the evaluation board. While validating a VCORE regulator it may be tempting to assume one capacitor is as good as another but from these results it’s recommended that that assumption be tested before moving onto production efforts. If sufficient margin is left in the design it may be true that one vendor’s components can be substituted for another. But in the case of switching from Vendor A to B this won’t hold. If additional footprints are not placed on the board, failures in the field or on the production floor may result. Taking the extra time to properly test a solution using several viable capacitors early on in the design phase saves time, effort, and cost. ■

Get the Datasheet and Order Samples http://www.intersil.com

Wide VIN 500mA Synchronous Buck Regulator ISL85415

Features

The ISL85415 is a 500mA Synchronous buck regulator with an input range of 3V to 36V. It provides an easy to use, high efficiency low BOM count solution for a variety of applications.

• Wide input voltage range 3V to 36V

The ISL85415 integrates both high-side and low-side NMOS FET's and features a PFM mode for improved efficiency at light loads. This feature can be disabled if forced PWM mode is desired. The part switches at a default frequency of 500kHz but may also be programmed using an external resistor from 300kHz to 2MHz. The ISL85415 has the ability to utilize internal or external compensation. By integrating both NMOS devices and providing internal configuration options, minimal external components are required, reducing BOM count and complexity of design. With the wide VIN range and reduced BOM the part provides an easy to implement design solution for a variety of applications while giving superior performance. It will provide a very robust design for high voltage Industrial applications as well as an efficient solution for battery powered applications. The part is available in a small Pb free 4mmx3mm DFN plastic package with an operation temperature range of -40°C to +125°C

• Synchronous Operation for high efficiency • No compensation required • Integrated High-side and Low-side NMOS devices • Selectable PFM or forced PWM mode at light loads • Internal fixed (500kHz) or adjustable Switching frequency 300kHz to 2MHz • Continuous output current up to 500mA • Internal or external Soft-start • Minimal external components required • Power-good and enable functions available.

Applications • Industrial control • Medical devices • Portable instrumentation • Distributed Power supplies • Cloud Infrastructure

Related Literature

TABLE 1. KEY DIFFERENCES BETWEEN PARTS

• See AN1859, “ISL85415EVAL1Z Wide VIN 500mA Synchronous Buck Regulator”

PART NUMBER ISL85415

TEMP RANGE (°C) -40°C to +125°C

ISL85415A -40°C to +85°C

EN THRESHOLD

PG DELAY

Standard TTL input

10% of soft-start time

High accuracy

2ms

NOTE: See Electrical specifications for more details on the ISL85415.

100 VIN = 15V

VIN = 12V

VIN = 5V

1 2

3 CBOOT 100nF CVIN 10µF VOUT COUT 10µF

L1 22µH

COMP

SYNC BOOT

FB GND

VIN

PHASE

PGND

12 11 R2 10 9

VCC

PG EN

R3 CVCC 1µF

CFB

EFFICIENCY (%)

90 85 80 75 70

VIN = 24V

VIN = 33V

60 55

INTERNAL DEFAULT PARAMETER SELECTION

0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 OUTPUT LOAD (A)

FIGURE 1. TYPICAL APPLICATION

September 5, 2013 FN8373.1

FIGURE 2. EFFICIENCY vs LOAD, PFM, VOUT = 3.3V

Intersil (and design) is a trademark owned by Intersil Americas LLC. Copyright Intersil Americas LLC 2013. All Rights Reserved. All other trademarks mentioned are the property of their respective owners.

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POW ER

INTEGRATIONS’

Qspeed

PRODUCT HIGHLIGHT

Diodes EEWeb Tech Trends takes a look at industry innovator Power Integrationsâ&#x20AC;&#x2122; new Qspeed family of silicon diodes.

y combining Schottky and P-N intrinsic structures, the Qspeed diode family from Power Integrations offers performance similar to expensive SiC (Silicon Carbide) Schottkys, but made in a standard low-cost silicon process. Qspeed diodes offer very low reverse recovery charge (QRR) and a soft recovery characteristic, making them ideal for applications such as Continuous Conduction Mode PFC and hard switching converters. The combination of very low QRR and soft recovery compared to ultra-fast diodes can lead to a more efficient design as well as lower EMI. Consequently, switching MOSFET and EMI filter size can be reduced for lower cost.

Power Developer Because of their soft recovery characteristic, Qspeed diodes make excellent output rectifiers, enabling designers to eliminate diode snubbers and gain efficiency.

Click below to watch an overview:

Desigers Take Note Standard Silicon diodes exhibit a sharp Q RR / temperature dependency leading to a rapid rise in reverse recovery loss as diode temperature rise. Qspeed diodes, with their relatively flat QRR/temperature dependency, are much more thermally stable. Because of their soft recovery characteristic, Qspeed diodes make excellent output rectifiers, enabling designers to eliminate diode snubbers and gain efficiency. And with QRR lower by up to 86% compared to ultrafast diodes, shoot-through current is greatly reduced leading to lower switching transistor loss.

PRODUCT HIGHLIGHT Series

Voltage

Current

H-Series

600 V

3-12 A

Q-Series X- Series

200, 300, 600 V 600 V

Feature Lowest switching loss

Benefit Highest Efficiency

3-60 A

Highest softness

Lowest EMI

3-20 A

Low Cost

BOM cost reduction

Qspeed diodes are available in the H-Series, Q-Series, and X-Series, allowing the designer to choose a diode having the characteristics best suited for a particular design.

Qspeed Applications and Design Support To assist designers in getting the most out of Qspeed diodes, Power Integrations offers design support including the interactive Qspeed Diode Selector, five informative videos, and of course, online and telephone applications support. Also provided are reference designs, PI Expert™ design software, the

PI Databook, PI University™, application notes, Apps TV, a list of component suppliers, design seminars, and rapid transformer samples. Qspeed Advanced Technology Brings SiC Performance to Cost Sensitive Designs According to Paul Lacey of Power Integrations, Qspeed

diodes use “three-dimensional mechanical features called p-wells offset by Schottky contacts to get the best of both PIN and Schottky junctions in the same device.” The result is a Silicon diode having high speed, low QRR, and high voltage capability similar to an expensive SiC Schottky process but using a standard low cost Si process.