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November 8, 2011
Laura Marlino Oak Ridge National Lab
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TA B L E O F C O N T E N T S TABLE OF CONTENTS
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Laura Marlino DIRECTOR, VEHICLE ELECTRIFICATION PARTNERSHIPS Interview with Laura Marlino - Oak Ridge National Lab
Featured Products Eliminating Unscheduled Hard Drive Downtime
8 10
BY GARY DROSSEL WITH WESTERN DIGITAL Learn how to save data by predicting when a storage device will fail.
A System Perspective on Specifying Electronic Power Supplies
15
BY BOB STOWE WITH TRUE POWER RESEARCH An introduction to the role of the electronic power supply, and how to match source power with specific applications.
RTZ - Return to Zero Comic
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INTERVIEW
Oakridge National Lab
Laura Marlino - Director, Vehicle Electrification Partnerships
I completed my bachelor’s at the University of New Mexico and went on from there to work at Teledyne Camera Systems in Acadia, California. I worked on analog electronics for a digital film conversion system, to store Hollywood films in a digital
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FEATURED INTERVIEW
Laura Marlino
How did you get into electronics/engineering and when did you start? I was originally attending the University of Tennessee and studying biology, of all things. In my junior year, it became clear to me that in order to do anything that I really wanted to do in biology, I was going to need a PhD. I wasn’t sure if I was genuinely interested enough in the subject to devote the time needed to achieve that, so I dropped out my junior year and enlisted in the Air Force. I decided that I wanted to travel, see the world, and do interesting things, like live overseas for a while. Well, I never got the opportunity to live overseas; I was stationed state-side the whole time. But I was trained in electronics in the Air Force, and that is how I originally got into this field. When I got discharged, I enrolled at the University of New Mexico to finish my bachelor’s degree. I had been stationed in Denver, Colorado and loved the area, and wanted to go to the University of Colorado. But of course anywhere I went would be out of state, and the University of Colorado was too expensive. New Mexico, however, a bordering state, was within the price range I could afford with the GI bill.
INTERVIEW
I went back to the University of Tennessee for my master’s, and when I graduated we were in a recession. Jobs weren’t plentiful, but I was able to get a position at Oak Ridge National Laboratory, working in electronics. I worked there for several years and then left to go work for a small start-up design company doing semiconductor design. The company was sold to Flextronics, at which time I left and returned to Oak Ridge National Labs and have been here ever since, now nearing 20 years.
It is a national laboratory; is it government-related research? We get the majority of our funding from the Department of Energy. With the funding we are tasked with looking at far reaching, long term, new technologies that the OEMs or suppliers don’t have the resources or luxury to look at. They are all tasked with, “What do we do to get to the next model?” We are looking at technologies for ten years down the line. Can you tell us a little bit about the research you are doing? Like I said, the majority of our funding comes from the Department of Energy, but we also work with companies directly. We do a lot of work with the automotive OEMs and Tier 1
What type of work do you do at Oak Ridge National Laboratory? For the past seven years I have been in hybrid electric vehicle technologies. We are the Department of Energy’s (DOE) premier power electronics and electric machines laboratory. We do novel, next generation designs for the electronics and the motors for hybrid, electric, and fuel cell vehicles.
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and 2 suppliers. Most of that work is on a proprietary level. The work that we do for the Department of Energy is all open to the public, since is it funded by tax dollars. Right now, I think the most exciting project we are working on is one for wireless power transfer for charging the large battery packs in electric and plugin hybrid vehicles. We got into this several years ago. It is sort of the buzz word now and everyone appears to be jumping on the bandwagon, but ORNL started back when very few people had ever even thought of it for vehicular applications. In the future, I feel that all electric and plugin hybrid cars will have this technology in them. With this technology, there is a receiving antenna on the underside of your car. You will
Evanescent high power wireless transfer antennas (receiving antenna on left and transmitting antenna on right)
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FEATURED INTERVIEW
format. At the time they had all of the movies on film, and after time the film degrades in the vaults so we had come up with an idea of how to digitize it all. I worked on doing that for a while and decided that California was way too expensive at the time, given my salary. I was married and my husband was having a hard time finding a job. We decided to move back to New Mexico where I got a job offer at Sperry, which later became Honeywell Aerospace and Marine Systems. I spent about six years there and decided that I wanted to go on for my master’s degree.
INTERVIEW
Oak Ridge is now taking the next step forward, which is probably a technology about 10 years down the line, where we are going to be embedding these coils in roadways. The DOE’s mission is to find ways to eliminate our dependency on foreign oil. To do that, we want to move toward the electrification of vehicles. We are working toward embedding charging coils in the road, and similar to a carpool lane, you will have a charging lane. As you drive your electric vehicle, you will be picking up a charge. You can enter the freeway with not quite a full charge, you will pick up charge as you drive down the lane, and you can exit with a fully charged battery. The car’s communications system will control whether the battery will receive a charge and will even be able to talk to your utility company to bill you for the electricity used. This will allow the downsizing of battery packs, making the cars lighter and more efficient, leading to cost reductions of these vehicles, accelerating them into the marketplace. What type of system is being used for this technology? It is a resonant system, which has inherent voltage isolation for safety. Since it operates at
resonance, it is going to draw very little power unless there is a matching antenna above the transmitting antenna. We are currently operating our system at about 20 kilohertz, though other companies are utilizing other frequencies. At Oak Ridge we are transmitting about five kilowatts of power across a 200250 millimeter gap between the two antennas with fairly high efficiencies. Believe it or not, this technology is moving so fast, there is now a standards committee that has been formed to establish wireless charging standards. I believe the targeted efficiency is 90 percent, from the wall to the battery. Have you been building prototypes? Yes, we have. We have a moving prototype demonstrator unit and we have been doing a lot of work on the antenna design this past year. Our demonstration unit is used primarily for testing our different design options. We are moving forward with plans to build our first ‘in motion’ charging prototype Do you test the difference between the moving and stationary antennas? Yes, our demonstration prototype has been fabricated so we can adjust alignment in three dimensions. One antenna is on a motorized track and we can test field coupling between the two antennas as a function of the antennas’ alignment. When moving one antenna over another, our demonstration test
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bed moves fairly slow. The station we have set up right now would represent stationary charging or what we call opportunity charging. Opportunity charging would be at red lights, stop signs, bus stops—any spot where you would momentarily stop your vehicle. While you are sitting there, waiting on traffic, your car would pick up a charge. Ideally, one of the first demos that we wanted to do was testing the system with shuttles at airports, which is a perfect fit for this technology. The vehicles routes are well-defined as well as where they will park. The buses or shuttles can charge their batteries while waiting for customers to load, drive the customers to their destination, and then sit and wait for additional customers while getting another charge. What size of an antenna is being used? The first one we began working on takes up most of the undercarriage of the car. It is about 36” x 40”. One problem is, where you build the matching antenna in your garage, or in a parking garage, will depend on knowing where the position of the antenna is in your car. The location and size of the antenna in the vehicle will need to be standardized, so whether they are pulling forward or backing into the parking space, they can position it correctly for maximum coupling. The goal is to develop an antenna that is about a 10” x 10” square that will be located under a car’s trunk. We are hoping to move to that, but right now the demo is just to test the science,
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FEATURED INTERVIEW
also have a transmitting antenna in your garage that is built into the concrete floor or part of a mat you can throw down on the floor. When you park your car in the garage, you will not have to plug it in to charge the battery; it will receive its charge from the transfer of power from the garage floor up into the car.
INTERVIEW
location, separations, and size. How much does the body of the vehicle impact the tuning of the antenna? There are shielding and EMI issues that are part of the ongoing work. What is your primary role in this project? I am the Director of Vehicle Electrification Partnerships at Oak Ridge National Laboratories. I oversee technical aspects of projects. Are there any other interesting projects that Oak Ridge is working on? One big issue is that most of the motors in hybrid vehicles have been using rare earth magnet materials. These motors have internal or surface magnets. The biggest supplier of these materials is China. We get about
97 percent from them. There is a big push to change this because China is so quickly becoming so technology driven that they are starting to use more of these materials in-house. The cost of the materials has doubled in the past year. The automobile industry is all about cost. We have new projects focusing on motor designs that do not use these rare earth magnets. Right now these rare earth machines have the highest power density of any motor utilized for hybrids. The trick is to develop motors that do not use the rare earth magnets but have the speed and torque characteristics of rare earth machines, as well as their efficiency and power density. We have a number of projects going on in this area. We are also looking at alternative permanent magnet motor technologies—ones that use different types of magnets,
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How hard is it for private industry to work with you on developing new technologies? We make it pretty easy for private industry to work with us. We have meetings twice a year and a review in Washington where industry people can come in. If they see technology that they are interested in and want to pursue, we offer licensing agreements so that we can promote getting these things out into the industry. That is ultimately our goal, to get technologies we develop out into commercial use. What challenges do you foresee in your industry? The market acceptance due to unproven reliability and high cost of electric vehicles. â–
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Matt Scudiere with evanescent high power wireless transfer antenna and initial instrumentation setup
not composed of rare earth materials. We are also looking at electromagnets to generate the electric fields. We are reexamining motor technologies that have been used for other applications, dismissed by OEMs because the rare earth permanent magnet machines perform so well. We are investigating ways to make these motors more effective. One technology is induction machines. They are the workhorse of the industry but they are bigger and heavier than the rare earth motors. There may be a case that can be made for induction machines in all electric vehicles. We think that we have a few ideas to make the induction motors more efficient and we are pursuing this research area.
F E AT U R E D P R O D U C T S The AD8428 is an ultra-low noise instrumentation amplifier designed for accurately measuring tiny, high-speed signals. It delivers industry3kΩ leading gain-accuracy, noise and bandwidth. All gain setting resistors for OUT 30.15Ω the AD8428 are internal to the part and precisely matched. Care is taken 3kΩ in both interconnects and symmetry. This results in excellent gain drift 120kΩ 6kΩ 6kΩ REF +IN and quick settling to the final gain value after the part is powered on. The AD8428 high CMRR of the AD8428 prevents unwanted signals from corrupting the –VS +FIL acquisition. The part’s pin-out is designed to avoid parasitic capacitance mismatches that can degrade CMRR at high frequencies. The AD8428 is one of the fastest instrumentation amplifiers available. The circuit architecture is designed for high bandwidth at high gain: it uses current feedback topology for the initial pre-amp gain stage of 200, followed by a difference amplifier stage of 10. This results in a 3.5 MHz bandwidth at a gain of 2000, for an equivalent gain-bandwidth product of 7 GHz. For more information, please click here. –IN
6kΩ
120kΩ
6kΩ
DIO1 DIO2 DIO3 DIO4 RST SELF-TEST
I/O
Ten Degrees of Freedom Inertial Sensor
VDD ALARMS
POWER MANAGEMENT
The ADIS16488 iSensor® MEMS IMU is a complete inertial system that includes a triaxis gyroscope, a triaxis accelerometer, triaxis magnetometer and pressure sensor. Each inertial sensor in the ADIS16488 combines industry-leading iMEMS® technology with signal conditioning that ADIS16488 optimizes dynamic performance. The factory calibration characterizes each sensor for sensitivity, bias, alignment, and linear acceleration (gyroscope bias). As a result, each sensor has its own dynamic compensation formulas that provide accurate sensor measurements. The ADIS16488 provides a simple, cost-effective method for integrating accurate, multiaxis inertial sensing into industrial systems, especially when compared with the complexity and investment associated with discrete designs. All necessary motion testing and calibration are part of the production process at the factory, greatly reducing system integration time. Tight orthogonal alignment simplifies inertial frame alignment in navigation systems. The SPI and register structure provide a simple interface for data collection and configuration control. For more information, please click here. TRIAXIAL GYRO TRIAXIAL ACCEL
CONTROLLLER
TRIAXIAL MAGN
CALIBRATION AND FILTERS
PRESSURE TEMP
CLOCK
OUTPUT DATA REGISTERS
GND
CS
SPI
USER CONTROL REGISTERS
SCLK DIN
DOUT
VDD
VDDRTC
Micropower Precision Voltage Reference The ADR3525W, ADR3530W, ADR3533W, ADR3540W, and ADR3550W are low cost, low power, high precision CMOS voltage references, featuring V SENSE a maximum TC of 5ppm/°C (B grade), low operating current, and low R GND FORCE output noise in an 8 lead MSOP package. For high accuracy, output R voltage and temperature coefficient are trimmed digitally during final assembly using Analog Devices, Inc., patented DigiTrim® technology. GND SENSE The low output voltage hysteresis and low long-term output voltage drift improve lifetime system accuracy. These CMOS are available in five output voltages, all of which are specified over the automotive temperature range of −40°C to +125°C. For more information, please click here. ENABLE
BAND GAP VOLTAGE REFERENCE
VBG
VOUT FORCE OUT
FB1
FB2
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FEATURED PRODUCTS
Low Noise Instrumentation Amplifier
–FIL
+VS
Avago Technologies LED Lighting Solutions
One LED. Infinite colors. World’s first waterproof package. Avago Technologies Tri-color High Brightness PLCC6 SMT LEDs gives you a reliable, long life product for ease of design in full color interior and exterior signs
Tri-color High Brightness SMT LEDs from Avago Technologies Avago’s PLCC-6 SMT LEDs are high brightness, high reliability, high performance, IPX6 compliant and are water and dust proof. They are designed with a separate heat path for each LED die, enabling it to be driven at higher current. They deliver super wide viewing angle at 120° together with the built in reflector pushing up the intensity of the light output.
Applications • Indoor and outdoor full color display • LED advertisement panels • Decorative lighting
Features • Water-resistance (IPX6*) per IEC 60529:2001 • Very small PLCC6 package dimensions – 3.4 x 2.8 x 1.8mm • In-line RGB dies configuration • Available in White Surface, Black-Surface and Full Black-Body • Wide operating temperature range: -40° to +110° For more information or to request a sample please go to:
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Eliminating Unscheduled Hard Drive Downtime Gary Drossel
Director of Product Planning
N
o matter how dependable the storage device, sooner or later it wears out. Often, this occurs without warning after tens of thousands of write/erase cycles. Unexpected drive failures can cause a complete disruption of business, resulting in costly downtime and a loss of data and customers. Until now, there has been no definitive way to predict when a storage device will fail. Western Digital (WD) developed Self-Monitoring Analysis and Reporting Technology (SiSMART) to help embedded OEMs avoid this problem. By constantly tracking a drive’s usage, SiSMART is able to report to the user the exact amount of useable life left on the drive. Drive usage information can be requested by the host at any time, and allows for an accurate prediction of the drive’s life. This is especially important during the qualification process. Users can take advantage of this information to set intervals for data collection, system maintenance, and drive replacement. This can save embedded OEMs upwards of hundreds of thousands of dollars a year in
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lost data, system downtime, and maintenance. WD SiliconDrive solid state storage technology is specifically designed to meet the high-performance, highreliability, and multi-year product lifecycle requirements of embedded OEMs in the netcom, military, industrial, interactive kiosk, and medical markets. With its key focus on decreasing the total cost of storage ownership over the entire system deployment, WD created technologies to minimize unscheduled downtime, maximize security for the OEM’s software IP, and provide real-time feedback to enable the host system to manage its storage more effectively. Applications requiring advanced levels of reliability and availability can employ WD’s patented SiSMART technology, which allows the host system to poll the SiliconDrive and receive real-time feedback as to the current usage. This technology allows the host to calculate projected remaining useable life and model the data transactions to ensure that the drive lasts throughout the scheduled deployment.
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TECHNICAL ARTICLE
The theory behind this command is that HDD failures do not usually occur suddenly. Most failures result from issues that generally occur over time, such as the mechanics of the HDD spindle wearing out. The SMART feature was designed to monitor such issues, which limits data loss and unscheduled system downtime. SiSMART for Monitoring Solid State Drives
Host System
Host Interface
Solid State Drives (SSDs) such as WD SiliconDrives do not have moving parts because they are solid state storage solutions, so many of the parameters monitored by the SMART function for HDDs are not applicable. Solid state drives are preferred in environmentally robust and high-duty cycle applications because they do not mechanically wear out, but there is still a concern about them degrading when exceeding the endurance specification.
Eliminating Unscheduled Downtime There are two ways to eliminate unscheduled downtime: • Develop technologies to prevent the failures and increase drive endurance. • Provide monitoring technology to warn the host system of impending issues. WD has engineered technologies that accomplish both of the following: • PowerArmor eliminates drive corruption due to power disturbances. • Solid state storage management algorithms such as advanced ECC and wear-leveling over the entire SiliconDrive maximize the drive operating life and extend system-level endurance.
Application Specific Technology
Solid-State Storage Management Algorithms
PowerArmor
SiSMART
SiliconDrive
Solid-State Storage Array
The Self-Monitoring Analysis and Reporting Technology (SMART) function was introduced in the American National Standards Institute’s (ANSI) release of the ATA-3 specification. Designed to act as an early warning system for pending problems with mechanical media such as hard disk drives (HDD), SMART technology works in conjunction with various sensors to monitor the HDD’s performance and determines whether or not performance is normal. The host system software can then poll the HDD using the SMART command and generate a flag to alert the user to a potential problem.
In much the same way a rechargeable battery loses its charge after several cycles, nonvolatile solid state storage components can lose their ability to retain data after tens of thousands of write/erase cycles. This is usually specified by component vendors as endurance. When a block loses its ability to retain data or when data errors occur that cannot be corrected by the drive’s ECC algorithm, the block is swapped with one from an available spare pool. When the spare blocks are exhausted and another error occurs, the solid state drive reaches critical failure and needs to be replaced. WD saw the need for a monitoring method for solid state drives and developed the SiSMART technology for SSDs.
Figure 1: Solid State Storage Technology
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SMART for Hard Drives
TECHNICAL ARTICLE
WD designed the SiSMART feature to monitor the write/ erase cycles of each block and the usage of spare blocks in SiliconDrive products. Monitoring both is essential in solid state drives that use wear-leveling to extend the life and endurance specification of the drive. Monitoring Spares Only There is a significant consideration when only using spares to determine remaining useable life in a solid state drive that does wear-leveling. Defined as the ability of the solid state drive to map logical block addresses to different physical blocks, wear-leveling evenly wears all of the blocks in the solid state drive if done properly, and all of the blocks should wear out at roughly the same time. The solid state drive has 100 percent of its spares available for most of the product life, and if a block wears out, it is replaced by a spare. The drive ceases to operate when the spares run out, so all of the spare blocks are used up at roughly the same time if they all wear out at roughly the same time (Figure 2).
100 80 60 40 20 0
Time
Figure 3: Percentage of SiliconeDrive Used Over Time
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SiSMART goes well beyond only monitoring spares. To yield meaningful information at any point in time, SiSMART tracks and tabulates write/erase transactions for each block in the SiliconDrive. Based on this information and whenever requested by the host, SiSMART can calculate the percentage of drive life remaining. If the used percentage goes beyond a certain comfort zone, the drive can be replaced during the next scheduled maintenance period. Eliminating unscheduled maintenance calls can save embedded OEMs tens to hundreds of thousands of dollars per year.
60
Modeling System Usage
SiSMART can provide the remaining number of spares to the host system at any time. The host can then set its threshold and take preventive action based on its own established set of criteria. 100
Percentage of Drive Used
Most system designers require a better feedback methodology that yields meaningful data at any time during system operation. It is useful to understand when the application has reached points such as 10%, 20%, 50%, and so on, that the host system can more accurately flag any issues in advance of when they are likely to occur (Figure 3).
Percentage of Spares Remaining
SiSMART technology performs an equally critical function by acting as an early warning system for the host and providing status on the percentage of drive usage relative to the endurance specification. The host can then set its threshold and schedule preventive maintenance before the system goes down unexpectedly.
Monitoring Data Transactions for Each Block
40 20 0
Time
Another benefit of the feedback provided by SiSMART is the ability to perform storage usage modeling. It is difficult for system designers to fully understand all data transactions between the host and the drive—especially if operating and file systems are used. SiSMART eliminates this uncertainty.
Figure 2: Percentage of Spares Remaining Over Time
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TECHNICAL ARTICLE
SiSMART
TECHNICAL ARTICLE An OEM that manufactures enterprise edge routers uses SiSMART to model the data storage requirements of its system. The router is constantly logging data, and write/ erase endurance is a significant issue. To properly size the SiliconDrive, the company had to review the data collection requirements. First, the company needed to determine which parameters to monitor and how often to log those parameters. Next, the company had to determine how long they wanted to deploy this product in the field—in this case, five years. The company had used flash cards in the past. The flash cards had no feedback mechanism and the company felt it would need to double the size of the card to give them the required comfort level for meeting the fiveyear deployment target. With SiSMART technology, the company deployed the capacity originally defined, resulting in immediate cost savings. The company tested the SiliconDrive in the field for six months and then brought the system back to the test lab and ran the SiSMART utility to determine drive usage. It turned out that the drive was less than five percent utilized, so the company not only felt comfortable with its current application, it found a new data reporting requirement and collected even more data, potentially giving it a competitive advantage in its market. The company could upgrade its system and still feel confident in meeting the five-year target. The SiSMART utility runs on Microsoft Windows XP/ Vista/7, Linux, or DOS-host systems. This executable utility can also be integrated into applications directly. Software libraries and source code is available under
NDA to those customers wanting to tailor this function to their unique requirements. Conclusion Traditional solid state drives and flash cards did not incorporate any type of feedback mechanism, and consequently were allowed to operate until they exceeded the endurance specification and failed. The ability to monitor write/erase endurance is analogous to monitoring fuel in an automobile. Having no monitoring solution is like driving the car without a fuel gauge. The system operates until it “runs out of gas.” Monitoring spares only is like having a light that comes on just before running out of gas. There may or may not be enough time “to get to a gas station” before the system fails. SiSMART monitoring technology is like having a complete fuel gauge. Preventive maintenance (“filling up”) in advance of a failure ensures the system operates properly and does not experience any unscheduled downtime. About the Author Gary Drossel is the director of product planning at Western Digital’s Solid State Storage Business Unit. Prior to the March 2009 acquisition of SiliconSystems by Western Digital, Drossel was the vice president of product planning at SiliconSystems. Previously, Drossel has also held various marketing, sales and field engineering management positions with SimpleTech, Motorola Computer Group’s Pro-Log division, and the industrial automation group of Parker Hannifin. Drossel graduated with a B.S. degree in Electrical and Computer Engineering from the University of Wisconsin. ■
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Example
Get the Datasheet and Order Samples http://www.intersil.com
2.5A Regulator with Integrated High-Side MOSFET for Synchronous Buck or Boost Buck Converter ISL85402
Features
The ISL85402 is a synchronous buck controller with a 125mΩ high-side MOSFET and low-side driver integrated. The ISL85402 supports a wide input voltage range from 3V to 36V. Regarding the output current capability from the thermal perspective, the ISL85402 can typically support continuous load of 2.5A under conditions of 5V VOUT, VIN range of 8V to 30V, 500kHz, +85°C ambient temperature with still air. For any specific application, the actual maximum output current depends upon the die temperature not exceeding +125°C with the power dissipated in the IC, which is related to input voltage, output voltage, duty cycle, switching frequency, board layout and ambient temperature, etc. Refer to “Output Current” on page 13 for more details. The ISL85402 has flexible selection of operation modes of forced PWM mode and PFM mode. In PFM mode, the quiescent input current is as low as 180µA (AUXVCC connected to VOUT). The load boundary between PFM and PWM can be programmed to cover wide applications.
• Ultra Wide Input Voltage Range 3V to 36V • Optional Mode Operation - Forced PWM Mode - Selectable PFM with Programmable PFM/PWM Boundary • 300µA IC Quiescent Current (PFM, No Load); 180µA Input Quiescent Current (PFM, No Load, VOUT Connected to AUXVCC) • Less than 3µA Standby Input Current (IC Disabled) • Operational Topologies - Synchronous Buck - Non-Synchronous Buck - Two-Stage Boost Buck • Programmable Frequency from 200kHz to 2.2MHz and Frequency Synchronization Capability • ±1% Tight Voltage Regulation Accuracy
The low-side driver can be either used to drive an external low-side MOSFET for a synchronous buck, or left unused for a standard non-synchronous buck. The low-side driver can also be used to drive a boost converter as a pre-regulator followed by a buck controlled by the same IC, which greatly expands the operating input voltage range down to 3V or lower (Refer to “Typical Application Schematic III - Boost Buck Converter” on page 5).
• Reliable Overcurrent Protection - Temperature Compensated Current Sense - Cycle-by-Cycle Current Limiting with Frequency Foldback - Hiccup Mode for Worst Case Short Condition • 20 Ld 4x4 QFN Package • Pb-Free (RoHS Compliant)
The ISL85402 offers the most robust current protections. It uses peak current mode control with cycle-by-cycle current limiting. It is implemented with frequency foldback under current limit condition; besides that, the hiccup overcurrent mode is also implemented to guarantee reliable operations under harsh short conditions. The ISL85402 has comprehensive protections against various faults including overvoltage and over-temperature protections, etc.
Applications • General Purpose • 24V Bus Power • Battery Power • Point of Load • Embedded Processor and I/O Supplies
100 95 VIN
SYNC AUXVCC VCC
VIN
BOOT ISL85402
ILIMIT
PHASE LGATE
SS EXT_BOOST FS SGND
VOUT
85
12V VIN
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36V VIN
24V VIN
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PGND
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6V VIN
90 EFFICIENCY (%)
PGOOD EN MODE
50 0.1m
1m
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100m
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FIGURE 1. TYPICAL APPLICATION
September 29, 2011 FN7640.0
FIGURE 2. EFFICIENCY, SYNCHRONOUS BUCK, PFM MODE, VOUT 5V, TA = +25°C Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2011 All Rights Reserved. All other trademarks mentioned are the property of their respective owners.
Bob Stowe
Power Supply Design Consultant
A System Perspective on Specifying Electronic Power Supplies Power Supplies Match Load to Source The world we live in provides us with commonly available sources of electrical power as well as endless types of sources yet to be discovered or developed. We also have countless applications for this power. However, the typical case is that the electrical power source is not in the adequate form to energize specific applications. There must be a matching process that changes the form of source power to useable power for applications. This matching process is the role of the electronic power supply. Notice that the phrase “electronic power supply� is a misnomer. Electronic power supplies do not create power; rather, they simply transform the available power from a source to a useful form for your application. Figure 1 illustrates the interactions between the source and the power supply and the power supply and the load.
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A Timely System-Level Approach Needed Approaching power supply application, specification, and design from a system-level perspective is of paramount importance for the success of projects. The system includes the source, the load, and the environment around the power supply. Additionally, the system power supply must be treated with equal weight as other aspects of the system design. Yes, the source and load characteristics must be known before the power supply requirements are determined. However, the time to evaluate power supply requirements is right after the initial load and source characteristics are known. It is quite common that a matching power supply design is not feasible given the initial load and source characteristic determination. In this case, either the load or source characteristics need to be adjusted before proceeding further with the system design. Otherwise, the result will be a failed project or a project with tremendous cost overruns. This
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Source of Power
Power Supply
(Not a perfect black box)
TECHNICAL ARTICLE
Solid lines represent a direct influence. Dashed lines represent indirect influence through the power supply.
Load
Desired Flow of Power Figure 1: Power Supply Interactions with the source and the load.
occurrence is a very common mistake that is easily prevented.
as the characteristics and limitations of the power supply itself.
A Major Cause of Project Failures
Upcoming Topics
Perhaps a reason for the common occurrence of project failure is a perception that electronic power supplies are the proverbial black boxes, capable of perfectly supplying power to the load. They are not perfect black boxes, and failure to consider their limitations and adverse behavior can be disastrous to a project program.
This series of articles about specifying power supplies from a system perspective will cover in more detail various aspects of system-level concerns. Following are some of these aspects to be covered: • Load Characterization • Source Characterization • Efficiency • Thermal Environment • Packaging
It is well known that the cost to make design changes increases exponentially with time in the development cycle. This exponential characteristic occurs due to the work that must be done to re-document, re-test, and re-work designs and existing products. Problems not found until late in the development cycle can prove to have disastrous cost consequences. Don’t be caught thinking that the power supply design can wait till the end! Design power supplies in your system at the right time. Power Supplies are Complex Electronic power supplies, especially switchmode type, have very complex mechanisms and require a diverse skill set to design. The skill set includes not just knowledge of high-frequency with high-power analog electronics, but also adequate knowledge of mechanical packaging and heat transfer concepts. Many vendors have done a good job of simplifying switching power supplies for general purpose applications. However, a system knowledge of the source and the load are still important as well EEWeb | Electrical Engineering Community
Watch for the upcoming articles on “A System Perspective on Specifying Electronic Power Supplies.” About the Author Bob Stowe has over 21 years of experience in various disciplines related to electronic energy conversion, possesses a master’s degree in power electronics, and is a member of IEEE in good standing. He also has obtained his certification in power electronics from the University of Colorado (COPEC). Additionally, he graduated from the United States Naval Academy in 1984 with a bachelor’s degree in electrical engineering, and served for five subsequent years as a United States Naval Officer. As a former military officer, he is familiar with military project requirements. Bob now works for True Power Research as a Power Supply Design consultant.■
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