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CONTENTS

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David Raun

PRESIDENT & CEO OF PLX A conversation about how PLX aims to serve rapidly growing data center and cloud environments with their PCIe-based products.

PLX’s PCIe-Based Data Center Fabric How ExpressFabric technology from PLX will change the way that data centers operate.

Featured Products This week’s latest products from EEWeb.

How to GaN

Electrical Charateristics of Enhancement Mode GaN Transistors

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Choosing a Video Card for Your PC

A guide to the variety of elements to consider when selecting a video card.

Renewable Storage at the Edge of the Grid

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Different approaches to energy grid resiliency during severe weather scenarios.

RTZ

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PLX Technology is an enterprise PCI Express silicon developer based in Sunnyvale,

The company’s broad product portfolio has helped them become market share leaders in PCI Exp switches and bridges, with additional leadership in USB and consumer storage controllers. PLX’ PCI Express switches are fundamental building blocks in many systems in conjunction with man market-leading CPU companies The company’s CEO, David Raun, joined the PLX team over eight years ago, bringing a strong background in semiconductor sales and marketing from a variety of Silicon Valley companies. We spoke with Raun about the key markets that PLX’s products serve, the company’s revolutionary ExpressFabric technology, and how this fabric will change the way data centers operate.

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INTERVIEW

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“We live by our core values of Leadership, Excellence, Integrity and Winning. We expect to win no matter who is considered our competitor.”

Could you sum up some of the products that PLX provides as well as what markets they serve? PLX’s main focus is PCI Express switches, in which we offer the industry’s broadest product line and service over 70 percent of the worldwide demand, making PLX the market leader. These products are a fundamental building block in many systems today as they route the PCI Express packets on, off and around boards. It is common for these products to be used in conjunction with CPUs from Intel, AMD, Cavium, and others. These devices range from four to 96 lanes today with each lane transferring up to 8Gbits/second at PCI Express Gen3 speeds. They create additional ports and are connected to many different products, including network controllers, storage devices and PCI Express slots. Currently we have over 50 different switches, with the latest 18 introduced supporting the highestperformance Gen 3 specification. A common configuration is four lanes together providing 32Gbits per second -- over three times the performance of 10Gigabit Ethernet. Designs using our 96-lane ExpressLane PEX8796 Gen3 switch realize throughput of up to 1.5 terabits per second -- performance that rivals all other interconnect technologies. Our largest markets include all the enterprise equipment that goes into today’s fast-growing data center or cloud environments. We sell to the top suppliers of enterprise storage, networking and servers. These customers include Cisco, EMC, Dell, HP, IBM, NetApp, Huawei, Fujitsu, NEC, and many others. Other markets include embedded applications like instrumentation and printers, as well as high-end PCs and graphic cards.

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In addition to the switches, the company offers multiple bridges that connect PCI Express to other interconnects like USB and PCI. These products have been proven, solid revenue generators for us for many years.

Do you see PLX expanding into any other areas? Yes, although we will continue to expand our current PCI Express switch product line to serve the needs of the market and our loyal customers including the next generation of PCI Express standard–Gen 4, at 16Gbps--we are deep into the development of an industry-disruptive new product line that services a changing data center market. This exciting new product line takes PCI Express “outside the box” as a fabric and opens up a much larger market for the company. Named ExpressFabric, this solution provides the lowest-cost and lowest-power solution at very high performance levels. The enterprise data centers serviced by companies like Cisco, IBM, EMC, Dell, and others, as well as the public cloud companies -- Google, Facebook, Amazon, and Microsoft, for example--are looking at new solutions to drop power and cost while increasing performance. ExpressFabric is a disruptive technology within the data center or public cloud because it can eliminate the traditional array of fabric controllers and switches currently found within the many server and storage racks. At about one-half the cost and one-half the power of alternative fabric schemes, ExpressFabric allows next-generation data centers to be built much more efficiently than with current architectures. PLX pioneered ExpressFabric technology and is providing major OEMs with the

INTERVIEW tools required to enable the technology to be fully adopted by a worldwide market.

with these companies to come up with new innovations in the form of storage-specific features embedded on our next-generation products.

Can you tell me a little more about PLX?

Looking forward five or so years from now, do you see any other IO interconnect technologies besides PCIe?

PLX Technology is a public NASDAQ company -- the ticker symbol is PLXT -- with sales of around $100 million per year. We are profitable and growing, and service all the top-five suppliers of servers, storage systems and networking equipment in each category. It is an exciting place to work with a culture focused on getting the job done and having some fun in the process. We have excellent talent throughout the company and everyone takes pride in what they do. We live by our core values of Leadership, Excellence, Integrity and Winning. We expect to win no matter who is considered our competitor.

“Inside the box,” where PLX has been mainly focused, is highly dominated by PCI Express. We are still in the early part of the Gen3 life with Gen 4 coming around 2016. This will carry the market as OEMs interconnect of choice most likely past the year 2020. There is not any industry-supported open IO standard that we are aware of expected to replace PCIe, alternative proposals are all proprietary. There is significant legacy software that runs on PCI and this will be hard to replace.

In what regional areas do you expect potential growth?

Today, the data center or cloud environment is a collection of servers, storage units and networking equipment all working together to make sure your iPhone, iPad or Google searches deliver the content you expect quickly. These data centers have hundreds if not thousands of these various enterprise products squeezed into a building, organized in rows of racks. Each one of these racks can contain 40-plus servers, storage units and networking switches. Today each of these individual units within the rack must talk to the outside world and to the other units within the rack so they are networked together using Ethernet, InfiniBand and/or Fibre Channel. This requires Ethernet NIC cards, Fibre Channel HBA cards or InfiniBand HCA cards. Although this is the traditional method used for many years, this solution is expensive and consumes significant power.

Most of our growth will come from our continued expansion in the data center and cloud. The design decisions are made predominately in the United States, Japan, Taiwan, and China. Most of the manufacturing is in China and Taiwan – both huge markets for PLX. Although we see some American companies starting to manufacture again in the U.S., we expect our greatest revenue growth to come from China.

Do you see PLX’s PCIe technology integrating with solid-state storage? Yes, this is a significant part of our business. The situation is that SSDs are becoming much more popular in the data centers. Most storage companies have already moved, or are quickly moving, to PCI Express-interface SSDs rather than SATA or SAS. They are doing this because PCI Express provides the highest performance, which is also why they are using SSDs in the first place. Almost all of the major OEMs have active programs where they are designing SSD systems that are PCIe-based. This is great for PLX as this drives demand for our switches. For every SSD drive or card that you put into the system, you need a PCI Express port, and many of these ports come from PLX switches. This is a large opportunity for PLX and it will be a significant growth factor for many years to come. We work closely

The other part of our future business is “outside the box,” with our ExpressFabric products. This solution will compete with Ethernet, InfiniBand and others interconnects.

Could you elaborate more on the ExpressFabric?

In the case of the ExpressFabric, we take advantage of the fact that PCI Express is already inside each of these systems. Unlike the other fabrics or interconnects mentioned above, PCI Express is coming directly off the CPU. The Intel Xeon product is a great example as it offers up to 40 lanes of PCI Express on each CPU but does not have 10Gigabit Ethernet, InfiniBand or Fibre Channel.

“We’ve had many customers tell us that they chose PLX over our competitors based on our support level.”

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PLX’s ExpressFabric Implementation

“ExpressFabric is a disruptive technology within the data center or public cloud because it can eliminate the traditional array of fabric controllers and switches currently found within the many server and storage racks.”

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With the PCIe rack-scale solution our customers save significant power and cost within the rack yet still take advantage of the greater Ethernet or InfiniBand network outside of the rack. We replace each of these with a simple $5 re-timer or switch offered by PLX. In addition to the cost savings, the power goes from 5-8 watts each to approximately 1 watt per device. Since there are 20 to 40 or more of these per rack, the savings add up quickly. Power costs in the data center are the largest expense, and can far exceed hardware costs. These PCI Express signals travel up to a PLX ExpressFabric switch, which replaces the current Ethernet, Fibre Chanel or InfiniBand switch. This switch supports host-to-host communication and provides I/O virtualization, where the Ethernet port at that top of the rack can be shared among the various components below. The ExpressFabric also enables the sharing of PCI Express SSDs discussed earlier at a very high performance level. Since the signal stays as PCI Express throughout the rack, there is no need to bridge over a fabric controller or create dedicated SSD storage for each server unit. This allows larger arrays of SSDs to be created and shared more cost effectively than the current approach.

INTERVIEW Keeping PCI Express as the fabric within the rack also supports nicely the GPGPU computing units where many graphic processors are used in parallel for high performance computing. Since the interface on these GPUs from companies like Nvidia and AMD are PCI Express, this supports this technology also very well. The nice thing about this rack-scale solution is power and cost savings at very high performance and the greater Ethernet or InfiniBand network remains as it ties the different racks together. As stated earlier the power and cost is about one-half and the performance is 32Gbps per x4 link, which is three times the performance of 10Gigabit Ethernet. Although we push PCI Express to the top of the rack and eliminate the need for one of these other fabrics within the rack, we will certainly co-exist with them beyond the rack. This is extremely disruptive technology that’s got the attention of major players. That’s why we are very excited and focused in this area.

Would PLX provide ICs to make this technology happen, or would you actually be building hardware for data centers? We build the ICs and provide software to allow our customers to build products to sell into the data center or cloud. Because this is a fabric, our customers want to see that it works, so we are building a top-of-the-rack switch box and PCI Express NIC cards. We’ll supply this to customers primarily to prove the technology and allow them to use it. It does allow us another revenue path down the road if we decide to, but our main focus today is to enable the market with the chips and software. I recently had my board of directors in, as well as an investor group, and we showed them a live demo. We already have a rack that demonstrates this capability, so it’s pretty exciting.

What length of cabling can be supported by PCIe? That’s part of the trick here. If you look at Ethernet, it’s designed to go 100 meters. Within a rack, you’re talking about something that needs three to five meters at the most. We

Top of the Rack Switch Box leverage the fact that PCIe will go this distance if you put the CPU close to the edge of the motherboard connection. If not, you need a $5 re-timer. Please keep in mind we are replacing something that is $50 to $500 and burns 5 to 8 watts. This is a big deal for data centers. Data centers usually spend more on electricity than they do on the equipment.

What kind of support does PLX provide for designers and developers? PLX is a big believer in customer support. We’ve had many customers tell us that they chose PLX over our competitors based on our support level. Our support comes in many different forms. First, we have a comprehensive website with many easily obtainable technical documents, application notes, white papers, presentations and videos. We also have a team of field application engineers throughout the world who are experts in this area. For example, things like signal integrity issues are a big deal when you are working at the high performance levels of our products. We work closely with customers to help find the sources of any problems and come up with solutions. Our products also ship with on-chip diagnostic tools that combine with a unique and free software development kit. These tools, named visionPAK, measure performance and utilize system debug features that allow customers to resolve issues very quickly and often avoid costly test equipment. This is a huge time-to-market advantage and superior to anything else offered in the industry. ■

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PLX’s

ExpressFabric

Creates a PCIe-based Data Center Fabric

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FEATURED ARTICLE

ith large-scale data centers becoming increasingly more important, there comes the need for a more-efficient method of interconnection. A closer look at these data center racks will reveal that they are connected via Ethernet or InfiniBand, requiring these boxes to convert data, which burns power and costs money. Due to its widespread adoption, PCI Express (PCIe) is an alternative to current solutions as a fabric for data center and cloud computing applications. PLX Technology has been explaining its ExpressFabric initiative, which will extend the reach of PCIe for use as a fabric in these larger data center applications. PLX aims to replace these costly bridges in data center racks with an affordable and reliable alternative solution.

Advantages of PCIe

PLX PCI Express-Based Fabric

When it is deployed, ExpressFabric will be implemented in cloud “micro-clusters” of between 20 and 1,000 CPU nodes, with most implementations within a single rack or small cluster. Through a PCIe convergence model that creates a single pathway for different data types, ExpressFabric allows for the elimination of protocol bridges that lead to unnecessary power and cost. PCIe connections can also be found in almost all storage devices, which means that no additional translation bridges are needed. The PCIe-based fabric will still smoothly co-exist with Ethernet, InfiniBand, and any other fabrics found in data centers where those standards will dominate rack-to-rack and long distance architectures. One of the main advantages of the omnipresence of PCIe is that it requires fewer components altogether, leading to lower latency, cost, and power. As CEO David Raun told us, “What PLX is doing with ExpressFabric is getting rid of that $50 to $500 NIC, HBA, or HCA and replacing it with a $5 part.” Essentially, PLX is offering an effective solution for half the cost and half the power.

hardware and software. “The network still stays there,” says Raun, adding “The end user leverages all of their applications and they do not have to change their software. All we do is take them from 1 or 10Gb of Ethernet up to 32Gb of PCIe.”

With a unified, PCIe-based fabric, I/O and storage subsystems are shared among the hosts, allowing for a clear, high-bandwidth path between all elements in the fabric. Because of normal oversubscription, the ability to share means that you actually need fewer I/O and storage devices for the same number of hosts, even further reducing the cost and power envelope of the system. Furthermore, ExpressFabric enables the use of preexisting

PLX is providing the market-seeding 1U switch box and the other necessary tools to effectively develop a PCIe-based data center fabric. The ExpressFabric development kit comes with a PCIe adapter card, a top-of-rack box, and a package of software drivers. The combination of these tools allow for easy migration to this new PCIe approach. Through this kit, users can become familiar with the necessary features for mass adoption of this technology. “This is extremely disruptive technology,” Raun told us, “We’ve already gotten the attention of major players. That’s why we are very excited and focused in this area.” ■

ExpressFabric in Microserver with SSD Array

Development Kit

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FEATURED PRODUCTS 83mm Phase Control Thyristors IXYS Corporation announced that its wholly owned UK subsidiary, IXYS UK Westcode Ltd., launched a new addition to its 83mm die phase control thyristors product group. The thyristors, rated at 2200 volt, are the latest introduction to this new product group that uses an integrated die construction and improved package design for better electromechanical and thermal performances. The 2.2kV thyristor has an average current rating (Case temperature 55C) of 4340 amperes, with a junction to heat sink thermal resistance of 0.008 kelvins per watt. The new thyristor is constructed using an all diffused silicon wafer slice fused to a metal header and encapsulated in a fully hermetic package. This construction enhances the performance and provides excellent transient thermal and surge current ratings...Read More

Power Management ICs Reduce Carbon Footprint Fujitsu Semiconductor America introduced its new FM4 family of 32-bit RISC microcontrollers based on the ARM® Cortex™-M4 processor core. The MCUs are designed for applications that require advanced, high-speed computing performance, such as general-purpose inverters, servomotors, PLCs and other industrial equipment, as well as energy-efficient, inverter-based home appliances. The new FM4 family includes 84 MCUs in its MB9B560R/460R/360R/160R series...Read More

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Technology You Can Trust

Avago Technologies Optocouplers

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TECH ARTICLE

Alex Lidow

CEO of Efficient Power Conversion (EPC)

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PULSE To read Part 1 of the series, click the image below:

For a power system designer who has worked with a power MOSFET, upgrading to an enhancement mode GaN transistor is straightforward. The basic operating characteristics are quite similar and yet there are a few characteristics that need to be considered in an efficient design in order to extract the maximum benefit from this new generation device.

Watch Out for These Electrical Characteristics Every semiconductor has a limit to its capabilities. These limits are typically expressed prominently in a device data sheet and serve as a guide to designers as to how to create designs that do not have hidden quality or reliability issues. Enhancement mode GaN transistors such as the eGaN® FETs from Efficient Power Conversion Corporation (EPC) have similar maximum ratings to commercial power MOSFETs except for the maximum allowed gate voltage. VGS (the voltage applied between gate and source) has a maximum of 6 V in the positive direction and 5 V in the negative direction. These values are relatively low compared with power MOSFETs and designers need to make certain their layouts do not have overshoot that takes the gate voltage beyond these limits. In general,

Figure 1: Normalized threshold voltage vs. temperature showing only a 3% change over the operating range of the EPC2010.

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this does not pose a significant problem because the FETs are fully enhanced at around 4 V. There have been several papers (Power Electronics magazine eGaN FET – Power Silicon Shoot Out series: Drivers, Layout; Impact of Parasitics on Performance; and, Optimal PCB Layout) written to help designers avoid this limitation, but perhaps the easiest solution is to use one of the commercially available gate driver ICs designed to protect the FET gate while extracting very short switching times. A typical power MOSFET has a threshold voltage (VGS(TH)) in the range of 2 – 4 V. For an eGaN FET, the VGS(TH) has a typical value of 1.4 V. However, unlike a power MOSFET, this threshold voltage is relatively insensitive to temperature as shown in Figure 1. This implies that an eGaN FET system’s noise immunity will not degrade with temperature as in a power MOSFET with even a higher starting VGS(TH). On-resistance (RDS(ON)) is the resistance of the eGaN FET when 5 V is applied from gate to source. The RDS(ON) will vary with both the gate voltage applied and the junction temperature of the device. Yet another advantage of eGaN technology over silicon is the lower increase in RDS(ON) with temperature as shown in Figure 2. Whereas silicon has about a 70% increase in RDS(ON) between 25°C and 100°C, the eGaN FET shows about 50% increase. This translates into roughly 15% lower RDS(ON) at a typical 100°C junction temperature assuming the same initial RDS(ON) at 25°C.

Reverse Diode As with a power MOSFET, the enhancement mode GaN transistor has the ability to conduct in the reverse direction. In the case of the GaN device, however, the physical mechanism is different. In a silicon power MOSFET, a p-n diode is integrated into the FET and conducts by injecting minority carriers into the drain region. This charge is stored in the drain region (QRR) for several tens of nanoseconds (tRR) and dissipated as heat when the diode is turned off. This is a significant disadvantage when you want to switch quickly. In an enhancement mode GaN transistor, the reverse conduction occurs because the FET electron channel turns on when there is a positive voltage between gate and drain electrodes. The channel instantly turns off when the voltage is removed without any stored charge to dissipate (tRR=0, QRR=0). There is an offsetting disadvantage however, in that the sourcedrain voltage drop across the device is higher than a comparable power MOSFET (see figure 3). In order minimize the impact of this higher Vsd drop and to get the best performance out of the eGaN FETs, it is necessary to keep the dead time to a minimum, enough to avoid cross conduction.

TECH ARTICLE A Big Benefit: Very Low Capacitance and Charge A FET’s capacitance is the biggest factor in determining the energy that will be lost in a device during a transition from the ON to OFF state, or from the OFF to the ON state. If you integrate the capacitance between two terminals across a range of voltage applied to the same terminals, you obtain the amount of charge “Q” that was required to charge the capacitor. Since current multiplied by time equals charge, it is often very convenient to look at the amount of charge necessary to determine the time to change the voltage across various terminals in the eGaN FET. Figure 4 shows the amount of gate charge, QG, which must be supplied to increase the voltage from gate to source to a desired voltage. In this figure there is a comparison between the 100 V, 5.6 mΩ (typical) eGaN FET and an 80 V, 4.7 mΩ (typical) power MOSFET. It takes about 1/4th the charge to fully enhance the eGaN FET. This translates into higher switching speeds and lower switching power losses.

Figure 2: Comparison between normalized RDS(ON) vs. temperature for the EPC2010 eGaN FET and various 200 V rated silicon MOSFETs.

Figures of Merit (FOM) To effectively compare the potential performance of a power MOSFET and an enhancement mode GaN transistor in a power conversion circuit, some figures of merit need to first be defined. A FOM that has been used by MOSFET manufacturers to show both generational improvements and to compare their products to other competitive devices is the product of the gate charge, QG, and the RDS(ON) for a given device. What makes this so useful is that no matter the size of the die, this FOM is almost constant for a given technology or ‘Generation’ of device. This FOM is related to device performance and can be useful in predicting power loss improvements with improved technologies, but it is less sensitive to differences when a device is used more as a switching element than as a conducting element. We will therefore discuss two distinct FOMs. The first of these is the traditional FOM. We will call that the “Rectifier FOM” because it is most applicable when a FET is used as a rectifier element such as in the lower transistor of a buck converter. The second FOM we will call the “Switching FOM” because it best describes relative performance of devices used mostly as switching elements such as in the upper transistor in a classic buck converter. Of these two FOMs, the switching performance is more important in ‘hard switching’ converter circuits.

Figure 3: Body-diode forward drop vs. source-drain current and temperature for an eGaN FET and for a power MOSFET.

Figure 4: Gate charge vs. gate voltage for the EPC2001 eGaN FET compared with competitors.

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PULSE Figure 5 plots RDS(ON) vs. QGD for eGaN FETs as well as for various equivalent silicon MOSFETs. We can see that, based on switching FOM, eGaN FETs offer a distinct advantage over any equivalent voltage rated silicon device. Below are some general observations: • 40 V eGaN FETs are comparable to 25 V lateral silicon devices. • 100 V eGaN FETs are comparable to 40 V vertical silicon devices • 200 V eGaN FETs are comparable to 100 V vertical silicon devices

Figure 5: RDS(ON) vs. QGD for various eGaN FETs and MOSFETs.

The rectifier FOM is shown in Figure 6 and plots RDS(ON) vs. QG for the eGaN FET as well as for different equivalent silicon MOSFETs. From this we can draw a number of conclusions: • 40 V eGaN FETs are comparable to the best 25 V lateral silicon devices. • 100 V eGaN FETs are comparable to 25 V vertical silicon devices • 200 V eGaN FETs are comparable to 40 V vertical silicon devices

The Ultimate Packaging Let’s now look at package-related comparisons between eGaN FETs and state-of-the-art MOSFETs.

Figure 6: RDS(ON) vs. QGD for various eGaN FETs and MOSFETs.

Semiconductor devices are packaged to improve robustness and ease of handling. Packaging, however, degrades performance compared to the bare semiconductor die in the form of increased on-resistance, increased inductance, increased size, and reduced thermal performance. Gallium nitride is self-isolating, meaning it protects itself from the environment because the active GaN element on top of a piece of silicon is actually encapsulated in a thick insulating glass. This characteristic of GaN permits EPC’s eGaN FETs to be packaged in a chipscale LGA format shown in figure 7. With this packaging, eGaN FETs have the smallest footprint, lowest package resistance, lowest package inductance, and highest intrinsic package thermal conductivity of any power package on the market.

Summary

Figure 7: EPC2001 eGaN FET in a chipscale LGA package. Package dimensions are approximately 4mm x 1.6mm

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In this column we discussed the basic electrical and mechanical characteristics of enhancement mode GaN transistors and showed they have many distinct advantages over current state-of-the-art silicon power MOSFETs. The silicon power MOSFET has come a long way since its introduction over thirty years ago, so it would be fair to assume that future optimization of the basic eGaN power transistor structure and geometry will show similar improvement in years to come. ■ eGaN is a registered trademark of Efficient Power Conversion Corporation.

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

Power Factor Correction Controllers ISL6730A, ISL6730B, ISL6730C, ISL6730D The ISL6730A, ISL6730B, ISL6730C, ISL6730D are active Features power factor correction (PFC) controller ICs that use a boost topology. (ISL6730B, ISL6730C, ISL6730D are Coming Soon.) The controllers are suitable for AC/DC power systems, up to 2kW and over the universal line input.

The ISL6730A, ISL6730B, ISL6730C, ISL6730D are operated in continuous current mode. Accurate input current shaping is achieved with a current error amplifier. A patent pending breakthrough negative capacitance technology minimizes zero crossing distortion and reduces the magnetic components size. The small external components result in a low cost design without sacrificing performance. The internally clamped 12.5V gate driver delivers 1.5A peak current to the external power MOSFET. The ISL6730A, ISL6730B, ISL6730C, ISL6730D provide a highly reliable system that is fully protected. Protection features include cycle-by-cycle overcurrent, over power limit, over-temperature, input brownout, output overvoltage and undervoltage protection.

• Reduce component size requirements - Enables smaller, thinner AC/DC adapters - Choke and cap size can be reduced by 66% - Lower cost of materials • Excellent power factor over line and load regulation - Internal current compensation - CCM Mode with Patent pending IP for smaller EMI filter • Better light load efficiency - Automatic pulse skipping - Programmable or automatic shutdown • High reliable design - Cycle-by-cycle current limit - Input average power limit - OVP and OTP protection - Input brownout protection

The ISL6730A, ISL6730B provide excellent power efficiency and transitions into a power saving skip mode during light load conditions, thus improving efficiency automatically. The ISL6730A, ISL6730B, ISL6730C, ISL6730D can be shut down by pulling the FB pin below 0.5V or grounding the BO pin. The ISL6730C, ISL6730D have no skip mode.

• Small 10 Ld MSOP package

Two switching frequency options are provided. The ISL6730B, ISL6730D switch at 62kHz, and the ISL6730A, ISL6730C switch at 124kHz.

• TV AC/DC power supply

• Desktop computer AC/DC adaptor • Laptop computer AC/DC adaptor • AC/DC brick converters

100

VI

VLINE

Applications

+

VOUT

95

EFFICIENCY (%)

90

VCC ISEN

GATE

ICOMP

GND

ISL6730

VIN

FB

ISL6730A, SKIP

80 ISL6730C

75 70

COMP BO

85

65

VREG

60

0

20

FIGURE 1. TYPICAL APPLICATION

40 60 OUTPUT POWER (W)

80

100

FIGURE 2. PFC EFFICIENCY

TABLE 1. KEY DIFFERENCES IN FAMILY OF ISL6730

February 26, 2013 FN8258.0

VERSION

ISL6730A

ISL6730B

ISL6730C

ISL6730D

Switching Frequency

124kHz

62kHz

124kHz

62kHz

Skip Mode

Yes-Fixed

Yes-Fixed

No

No

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

PULSE

Computer hardware is a very interesting topic, especially when constructing Rob Riemen Computer Engineering Student at the University of Cincinnati

your own computer. In previous articles I have discussed how to choose a processor based on electrical characteristics, and then how to pick out a mother board based on both this predetermined processor and the motherboard’s electrical characteristics. The next important topic on your path to building your very own computer is selecting your video card (or graphics card).

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TECH ARTICLE

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PULSE

I expect that you are choosing to build a computer because you want to use your computer for a very specific purpose. If you wanted to just browse the internet and listen to music from your computer there are plenty of cost-efficient computers already available for purchase. But when you build your own computer, and you budget correctly, you can create a computer for any need. Video cards fit in as a very important part of your computer. When figuring out how you want to use your computer, choosing the right video card makes all the difference. If processing power is what you need and the applications you want your computer for have few graphical requirements, then a lower end video card would be the best bang for your buck. If the task you need your computer to perform is is gaming, or video editing, then a higher-end card is a must. In order to highlight the other important characteristics of a video card, it is best to demo the higher end cards, as they show significant improvements in performance. This is because their specifications are stronger. Video cards are the graphical workhorse of your computer. These cards power the screen you are viewing to read this article. They display the internet browser you are using. The process the YouTube video you are watching. They render the 3D graphics needed to play your favorite game. All these functions make them crucial for the performance of the computer. But, what makes them tick? What electrical characteristics make a difference in the selection of these cards? In order to answer these questions we have to take a look at how the graphic cards are made. A graphics card can actually be considered a mini-computer. These cards contain processors, called Graphical Processing Units (GPU), video and Random Access Memory (RAM), bridges and data busses, and outputs -- in order to connect to other components. All of these components work together to provide the graphical quality you see on your

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screen. Of these components, it is actually simple to find three main characteristics that make the most difference in performance and efficiency in selection. The processor and the motherboard are specifically designed to handle certain other tasks, but neither are designed to handle graphical processing, which is a a special type of computer function requiring a different setup than a standard computer. This makes the GPU and video memory the most important specifications when selecting a video card.

Graphical Processing Unit (GPU) According to Wikipedia, a GPU, “is a specialized electronic circuit designed to rapidly manipulate and alter memory to accelerate the building of images in a frame buffer intended for output to a display” (Wikipedia 2). In reference to the name, it is the “processor” of the graphics card. The transistors that make up this processor do calculations that work on rendering the graphics shown on your display. The functions it helps manipulate include texture mapping, rendering polygons, and accelerating geometric calculations. These geometric calculations include rotation and translation of vertices into different coordinate systems. Just like a computer processor, the GPU is made up of millions to billions of tiny transistors that work together to translate voltage high’s and low’s into readable data to the computer. As mentioned prior, the transistors are positioned in a way that help in the graphical functions that are key to Desktop and 3D rendering. Along with the construction of transistors, two frequency clocks are used in all GPU’s. The clocks that are of concern in GPU’s are the Core Clock and the Memory Clock. These clocks are constructed in the same way as a processor core clock. A frequency crystal vibrates at a certain speed to increase the processing time of instructions sent to the GPU. Today’s high end GPU’s, Nvidia’s GeForce GTX 680 and AMD Radeon HD 7970, run with a core clock around 900 Mhz and with a memory clock between

TECH ARTICLE 1 GHz and 6 GHz. The higher number is usually the best to choose as the processor can then execute more instructions. When selection your graphics card, take a look into the design of the GPU and the clock speeds as these will be the most important in you decision based on performance and efficiency.

Video Memory The memory clock is integral to the design of the GPU, but it mostly functions more with the video memory. Memory on a video card functions in the same way as memory in a computer. It is a storage device for information used by the GPU. It uses the memory clock described previously to cycle through the memory buffer and execute the data in the correct order needed by the GPU. So, when picking a graphics card based on the video memory, more will almost always be better. The more space the video card has to process means better functionality overall. The voltage high’s and low’s that are processed by the GPU will be stored in this memory. In order to handle the amount of data that is processed by contemporary video cards, special types of memory have been developed. Today’s video cards use a faster memory interface called Graphics Double Data Rate, version 5 or GDDR5. Wikipedia’s definition describes GDDR5 as, “a type of high performance DRAM graphics card memory designed for computer applications requiring high bandwidth” (Wikipedia 1). Such memory helps in storing large amounts of data like that with the screen image and the Z-buffer. In order to access that information, there has to be an instruction set that helps process the right information at the right time. This is where the memory clock comes in. The memory clock sets the frequency in which the instruction set is executed. The higher the memory clock, the faster the GPU can access the information it needs that is stored in the memory. In conjunction, the memory of the graphics card plays a large role in performance and efficiency. It is a general rule that when in doubt choose larger space for memory and higher frequency for memory clock.

Conclusion Graphics cards play a huge role in the operation of a computer system. Without some type of GPU, there would be no visual display. With graphics cards getting that much more expansive it is hard to single out the electrical specifications that make a difference when selecting the right graphics card. To make it more inclusive, the most important component of the graphics card is the GPU. It is the heart and soul of a graphics card and handles all of the technical calculations needed to render visual displays. It is important to note the core clock speed, the memory clock speed, and the current design of the GPU architecture. The memory clock speed relates to how the GPU stores data. The video memory of the graphics card stores the information processed by the GPU for later use. In order to effectively access this data, the memory clock processes the instruction set needed to get the data. The higher the memory clock, the faster the access to the data. The larger the video memory, the more space the GPU has to store data. Keep this in mind in your next custom build computer in order to maximize performance and efficiency. ■

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PULSE

Richard Fioravanti

Vice President, Distributed Energy Resources DNV KEMA Energy & Sustainability

O

ver the last three years, util outages that have attracted impact of reliability has always simply as inconveniences, rathe typical outage profile that most in rare cases, an hour or two. T reliability, and utilities are conti

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TECH ARTICLE

lity customers have observed or been impacted by weather-related, long term d increasing attention to the concept of reliability and resiliency. The monetary been a challenge to quantify for the typical, small end-user; often being thought of er than an impactful disruption to everyday activities. This attitude develops from the t consumers are exposed to; one which has a duration range from momentary to, Tracking, improving, and reducing the number of these incidences is categorized as inually striving to eliminate them from our lives.

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H

owever, as severe storms or widespread disruptions create instances of long-term outages with durations of days, the concept of reliability transforms into one of resiliency. With this transformation, different approaches and solutions must be considered to prevent scenarios that were once considered rare, but are now considered an eventuality for any grid.

Solutions: What’s the best option? When examining the potential set of solutions, options such as traditional, fossilfueled generation are the first choices to be proposed. However, space and environmental considerations may prevent this solution from being an option. In addition, for the severity of incidences that has been recently witnessed, resiliency of the fuel infrastructure may end up being just as problematic as resiliency of the electricity infrastructure. For this article, the focus is on a more selfcontained solution of distributed, renewable generation combined with storage systems. Targeting the edge of the grid for this solution, a comparison will be made to examine the two locational options for this potential solution – on the utility side of the fence or on the customer side of the fence. Many owners of solar systems are often surprised to learn – often it is only when they have no power – that that solar device they paid for doesn’t work during an outage. This lesson is typically hardest when an outage occurs over multiple hours and days, when households need to make it through a night without power and heat. The solution to this issue is technically feasible, but often not adopted due to cost. It essentially involves “islanding” your system to isolate your solar system from the grid and allow power to flow directly into a home or building and then adding an electricity storage device that is able to charge during the day and discharge during the evening. This solution gets a little

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more complex when it is realized that to keep such a system economically attainable, critical loads need to be separated from the total load -- so during the outage, a balance of generating, supplying and charging, and then discharging during nighttime hours can be achieved. Sizing the storage device correctly is key to maintaining critical loads but also to keep the battery costs reasonable.

Utility Storage Solutions Today, utilities are already demonstrating, testing, and deploying concepts such as distribution storage and community energy storage (CES). With this concept in place, it would not be a “leap” to target this resiliency solution sited on the “utility” side of the fence. Of course, having the battery already there solves a reliability problem, but most likely will not solve a resiliency problem. For a widespread, long duration outage, there is the risk of the storage solution simply draining its charge after one day and leaving endusers in the same predicament. Hence, this solution needs to be coupled with the ability to charge the devices that are already in place. For CES systems there is the potential to utilize the renewable systems that are at the very edge of the grid, or if it is distributed storage, a larger solar installation could be employed. There may be a number of advantages of this approach. However, it’s not an easy task to have the proper regulatory policies in place that allow utilities and residences to access and share components of essentially the same system located on “both sides of the fence.”

TECH ARTICLE

Customer Storage Solutions As stakeholders begin to tackle the “resiliency” issue, the type of solutions that are being described here are under the spotlight. However, work still needs to be done in order to select the best option to site the solution, customize the “system” for siting on the utility side of the meter, or self-contain it at the site of small commercial buildings or residences. An example of one of the potential solutions is shown in the figure above, where the home has a solar panel, a transfer switch to “island” the home critical locals during the outage, and a storage device to provide power during evening hours. The profile on the right shows that under this scenario, the solar panels are able to supply “critical” loads during the day as well as charge the storage device. The “gold” portion in the chart shows “excess” capacity under such a scenario that would be used to charge the battery. In the evening, the storage device would discharge to the critical loads, thus providing a sustainable system that could keep critical loads operating throughout the outage.

greater access to these systems. Also, as stated, this concept doesn’t have to be located only on the customer side of the grid. Similar approaches can also be adopted by utilities to serve multiple homes.

Moving Forward In the end, it is clear that stakeholders and operators of the grid need to account for scenarios that were once considered extremely rare, but now are being witnessed with increasing frequency – demonstrating how long term outages can have devastating impacts on our society. The solutions and technologies are available today to make our grid more resilient and able to withstand such shocks, but the best option certainly has not been determined. Continued work is necessary with respect to packaging the systems for utilities and end users, as well as properly sizing, and locating the system. The best solution may be one system that is shared by the utility and the end-user, where the utility and end-user have access to the system, shares the benefits and cost of the solution in order to accelerate implementation. Though this is a potentially elegant option, it is one that will also require regulatory changes, better controls, utilities and end-users jointly agreeing on priorities of the system. ■

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