Ten Tips For Successfully Designing With Automotive EMC .

3y ago
43 Views
2 Downloads
380.60 KB
5 Pages
Last View : 28d ago
Last Download : 3m ago
Upload by : Fiona Harless
Transcription

Analog Applications JournalAutomotiveTen tips for successfully designing withautomotive EMC/EMI requirementsBy Mark SauerwaldApplications Engineer, Automotive Connectivity and EthernetIntroductionFigure 1. Typical testing chamber with specialconical tiles to stop reflectionsThe automotive industry and individual automobile manufacturers must meet a variety of electromagnetic compatibility (EMC) requirements. For example, two requirementsare to ensure that electronic systems do not emit excessive electromagnetic interference (EMI) or noise, and tobe immune to the noise emitted by other systems. Thisarticle explores some of these requirements and offerssome tips and techniques that can be used to ensure thatequipment designs are compliant with these requirements.Overview of the requirements for EMCCISPR 25 is a standard that presents several test methodswith suggested limits to evaluate the level of radiatedemissions from a component to be installed in a vehicle.[1, 2]In addition to the guidance that CISPR 25 provides tomanufacturers, most manufacturers have their own set ofstandards to augment the CISPR 25 guidelines. Theprimary purpose of CISPR 25 testing is to ensure that thecomponent to be installed in the automobile will not interfere with other systems within the vehicle,CISPR 25 requires that the electromagnetic noise levelin the room where the test is performed must be at least6 dB lower than the lowest levels being measured. SinceCISPR 25 has places where it looks for levels as low as18 dB (µV/m), an ambient level of less than 12 dB (µV/m)is needed. As reference, this is approximately the fieldstrength for a typical AM radio station, 1 km from theantenna.[3]In today’s environment, the only way to meet thisrequirement is to perform testing in a special chamberthat is designed and built to shield the testing environment from outside fields. Additionally, since normalbudgets require that the chamber be of finite size, it isimportant to protect the testing environment from reflections of signals generated within the room. Therefore,test-chamber walls must be lined with a material that willnot reflect electromagnetic (EM) waves (Figure 1). Testchambers are expensive and typically rented by the hour.To save costs, it is a good idea to evaluate EMC/EMI issuesduring the design phase to achieve first-time success inthe chamber.Another testing standard is the ISO 11452-4 BulkCurrent Injection (BCI) suite of tests that are used toverify if a component is adversely affected by narrow-bandelectromagnetic fields. Testing is done by inducing disturbance signals directly into the wiring harnesses with acurrent probe.Texas Instruments10 tips for successful EMC testing1. Keep loops smallWhen a magnetic field is present, a loop of conductivematerial acts as an antenna and converts the magneticfield into a current flowing around the loop. The strengthof the current is proportional to the area of the enclosedloop. Therefore, as much as possible, keep loops fromexisting, and keep any required enclosed areas as small aspossible. An example of a loop that might exist is whenthere is a differential data signal. A loop can form betweenthe transmitter and the receiver with the differential lines.Another common loop is when two subsystems share acircuit, perhaps a display and an engine control unit(ECU) that drives the display. There is a common ground(GND) connection in the chassis of the vehicle—a connection to this GND at the display end and at the ECU end ofthe system. When the video signal is connected to thedisplay with its own ground wire, it can create one hugeloop within the ground plane. In some cases, a loop likethis is unavoidable. However, by introducing an inductoror a ferrite bead in the connection to ground, a DC loopcan still exist, but from an RF emissions standpoint, theloop is broken.Also, a loop is formed by every differential driver/receiverpair when a signal is sent over the twisted-pair cable.Generally, this loop has a small area for the cable portionof the link because the twisted-pair is tightly coupled.However, once the signal gets to the board, close couplingshould be maintained to avoid opening up the loop area.4AAJ 3Q 2015

Analog Applications JournalAutomotive2. Bypass capacitors are essentialportion of the circuit. It may still emit energy, but goodshielding can capture the emissions and send them toground before they escape from the system. Figure 2 illustrates how shielding can control EMI.Shielding can take a variety of forms. It might be assimple as enclosing a system in a conductive case, or itcould involve fashioning small custom metal enclosuresthat are soldered over emission sources.CMOS circuits are very popular, in part, because of theirhigh speed and very-low power dissipation. An ideal CMOScircuit only dissipates power when it is changing statesand when the node capacitances need to be charged ordischarged. From a power-supply standpoint, a CMOScircuit that requires 10 mA on average may be drawingmany times that during clock transitions, then little or nocurrent between cycles. Therefore, emission-limiting techniques are focused on peak voltage and current valuesrather than average.Current surging from the power supply to the power pinon a chip during clock transition is a prime source foremissions. By placing a bypass capacitor close to eachpower pin, the current required to supply the chip duringthe clock edge comes directly from the capacitor. Thenthe charge on the cap builds up with a lower, steadiercurrent between cycles. Larger capacitors are good forsupplying large surges of current, but tend to react poorlyto very high-speed demands. Very small capacitors canreact quickly to demand, but their total charge capacity islimited and can quickly become exhausted. The best solution for most circuits is to use a mix of different-sizedcapacitors in parallel, perhaps 1-µF and 0.01-µF capacitorsin parallel. Place smaller size capacitors very close to thechip’s power pins, while larger-sized capacitors can beplaced further away.Figure 2. Example of shielding100 V –(a) Typical EMI problem3. Good impedance matching minimizes EMI–When a high-speed signal is sent through a transmissionline and it encounters a change in the characteristicimpedance on that line, part of the signal is reflected backto the source of the signal and part continues along in theoriginal direction. Invariably, the reflection leads to emissions. For low EMI, good high-speed design practice is anecessity. There are a plethora of good sources for transmission-line design information.[4, 5] Here are somesuggested precautions when designing transmission lines: Remember that the signal exists between the groundplane and the signal trace. Emissions can be caused byan interruption in either the signal trace or the groundplane, so pay attention to ground plane cutouts or discontinuities beneath the signal trace. Try to avoid sharp angles on the signal trace. Nicelycurved corners are much better than right-angle turns. Often times, an FPD-Link signal will have componentstapped off of it; such as power over coaxial cable, powerconnections, AC-coupling caps, and many others. Tominimize the reflections at the components, try to usesmall components such as 0402 size and set the width ofthe trace to be the same as the width of the 0402 component pad. Also, be sure to set the characteristicimpedance of the trace by controlling the dielectricthickness in the stackup.–––––– – – ––(a)––––––100 V – E 0V (b) EMI controlled with shielding5. Short ground connectionsEvery bit of current that flows into a chip flows back outagain. Several tips in this article discuss having shortconnections to the chip—bypass capacitors close to theIC, keeping loops small, etc. However, often forgotten isthe path that the ground current has to take to get back toits source. In an ideal situation, a layer of the board isdedicated to ground and the path to GND is not muchlonger than a via. However, some board layouts havecutouts in ground planes that can force ground currents totake a long path from the chip back to the power source.While the GND current is taking this path, it is acting asan antenna to transmit or receive noise.4. ShieldingDon’t shortcut good shielding techniques. When designingto minimize emissions, put a shield around the offendingTexas InstrumentsE 10 V5AAJ 3Q 2015

Analog Applications JournalAutomotive6. No faster than needed10. Spread-spectrum clocking reduces peak emissionsThere is a tendency to worry about timing margins and touse the fastest logic possible to provide the best timingmargins. Unfortunately, very fast logic has sharp edgeswith very high-frequency content that tends to produceEMI. One way to reduce the amount of system EMI is touse the slowest logic possible that will still meet timingrequirements. Many FPGAs allow programming the drivestrength at lower levels, which is one way to slow the edgerates. In some cases, series resistors on logic lines can beused to decrease the slew rates of signals in the system.With components such as FPD-Link serializers and deserializers (SerDes), there is often a data bus and clock thathave the option of spread-spectrum clocking. In spreadspectrum clocking, the clock signal is modulated. Theresult is that energy generated by the edges of the clockand data signals is spread across a wider frequency bandthan it would otherwise occupy. Since EMI specificationsare set to limit peak emissions at any frequency within aband, spreading noise across a wider band can help tominimize the noise peaks .A good example of a deserializer is the DS90UB914A-Q1,which is often used in conjunction with the DS90UB913A-Q1serializer. These devices are used to provide a video linkbetween a camera in an advanced driver assistance system(ADAS) and the processor. The deserializer recovers theclock that the image sensor in the camera provided to theserializer and outputs this clock along with the data foruse by the processor. Ten or 12 high-speed data lines thattransition concurrently with a high-speed clock are aprime source of EMI. To mitigate this EMI, the DS90UB914Ahas an option to use a spread-spectrum clock with theoutput data, rather than the lower-jitter clock that theimage sensor provides. The spread-spectrum clock iscontrolled through registers in the deserializer.7. Supply line inductorsTip #2 discussed bypass capacitors as a way to decreasethe impact of current surges. Inductors on the supply linesare another side of the same coin. By placing an inductoror ferrite bead on a power-supply line, it forces the circuitsconnected to that supply to draw their dynamic powerrequirements from the bypass capacitors, rather than allthe way back from the power source.8. Caps at inputs to switching suppliesOne recurring theme when looking to solve EMI issues isto reduce dv/dt and/or di/dt wherever possible. In thiscontext, DC/DC converters may seem completely harmlessuntil it is realized that they don’t convert directly from DCto DC. Rather, they go from DC to AC to DC. Hence, theAC in the middle has the potential to cause EMI problems.One area where automotive designers are concernedabout creating interference is in the AM radio band. Mostevery automobile is equipped with an AM radio, which hasa very sensitive, high-gain amplifier tunable from 500 kHzto 1.5 MHz. If a component is emitting a signal within thisband, it will probably be audible on the AM radio. Manyswitching power supplies use switching frequencies withinthis same band, which leads to issues in automotive applications. As a result, most automotive-switching suppliesuse switching frequencies that are above this band—oftenat 2 MHz or higher. If there is insufficient filtering either atthe input or the output of a switching power supply, someof this switching noise may find its way into other subsystems that may be sensitive to the root or subharmonicfrequencies.ConclusionAs automobiles rely more on electronics for critical vehicleoperation in addition to entertainment and comfort functions, there is a growing need to operate without error inthe presence of interference and to not provide interference to other systems within the vehicle. By following thetips and techniques outlined in this article, and throughselection of appropriate components, engineers are able todesign robust systems that enable automotive systems tooperate reliability without EMI problems.References1. CISPR 25 specification, ANSI eStandards Store2. Vincente Rodriguez, “Automotive Component EMCTesting: CISPR 25, ISO 11452-2 and equivalentStandards,” Safety & EMC 20113. AM Broadcast Groundwave Field Strength Graphs, FCCEncyclopedia4. Brian C. Wadell, “Transmission Line Design Handbook,”Artech House, Jan 1, 19915. Howard W Johnson and Martin Graham, “High SpeedSignal Propagation: Advanced Black Magic,” PrenticeHall Professional, 20039. Watch for resonancesFor various sources of interference, inductors and capacitors have been prescribed to tame the dv/dt and di/dt evilsthat can lead to EMI. However, inductors and/or capacitorscan have undesirable characteristics related to self resonance. This problem can often be rectified by adding aresistor in parallel to the inductor to absorb the energy ofthe oscillation before it becomes big enough to causeissues. Another potential issue is when there is a seriesinductor, either a discrete component or a parasitic inductance from a power line, that leads to a component with abypass capacitor. The resulting L-C circuit has the potential to oscillate at the resonant frequency. Once again, thiscan be tamed with a resistor, often placed in parallel withthe inductor.Texas InstrumentsRelated Web sitesProduct information:DS90UB914A-Q1DS90UB913A-Q1Subscribe to the AAJ:www.ti.com/subscribe-aaj6AAJ 3Q 2015

Analog Applications JournalTI Worldwide Technical SupportInternetTI Semiconductor Product Information CenterHome Pagesupport.ti.comTI E2E Community Home Pagee2e.ti.comProduct Information CentersAmericas Phone 1(512) 0-7544FaxInternet/Email 1(972) 927-6377support.ti.com/sc/pic/americas.htmEurope, Middle East, and AfricaPhoneEuropean Free CallInternationalRussian Support00800-ASK-TEXAS(00800 275 83927) 49 (0) 8161 80 2121 7 (4) 95 98 10 701 Note: The European Free Call (Toll Free) number is not active inall countries. If you have technical difficulty calling the free callnumber, please use the international number above.FaxInternetDirect Email (49) (0) 8161 80 rnationalDomestic co.jp/pic 2015 Texas Instruments Incorporated. All rights reserved.AsiaPhoneToll-Free Number Note: Toll-free numbers may not supportmobile and IP phones.Australia1-800-999-084China800-820-8682Hong New 6-0010International 86-21-23073444Fax 86-21-23073686Email tiasia@ti.com or htmImportant Notice: The products and services of Texas InstrumentsIncorporated and its subsidiaries described herein are sold subject to TI’sstandard terms and conditions of sale. Customers are advised to obtain themost current and complete information about TI products and servicesbefore placing orders. TI assumes no liability for applications assistance,customer’s applications or product designs, software performance, orinfringement of patents. The publication of information regarding any othercompany’s products or services does not constitute TI’s approval, warrantyor endorsement thereof.A021014E2E is a trademark of Texas Instruments. All other trademarks are the property oftheir respective owners.SLYT636

IMPORTANT NOTICETexas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and otherchanges to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latestissue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current andcomplete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of salesupplied at the time of order acknowledgment.TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s termsand conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessaryto support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarilyperformed.TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products andapplications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provideadequate design and operating safeguards.TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, orother intellectual property right relating to any combination, machine, or process in which TI components or services are used. Informationpublished by TI regarding third-party products or services does not constitute a license to use such products or services or a warranty orendorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of thethird party, or a license from TI under the patents or other intellectual property of TI.Reproduction of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alterationand is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such altereddocumentation. Information of third parties may be subject to additional restrictions.Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or servicevoids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice.TI is not responsible or liable for any such statements.Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirementsconcerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or supportthat may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards whichanticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might causeharm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the useof any TI components in safety-critical applications.In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is tohelp enable customers to design and create their own end-product solutions that meet applicable functional safety standards andrequirements. Nonetheless, such components are subject to these terms.No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the partieshave executed a special agreement specifically governing such use.Only those TI components which TI has specifically designated as mili

automotive EMC/EMI requirements Introduction The automotive industry and individual automobile manu-facturers must meet a variety of electromagnetic compati-bility (EMC) requirements. For example, two requirements are to ensure that electronic systems do not emit exces-sive electromagnetic interference (EMI) or noise, and to be immune to the noise emitted by other systems. This article .

Related Documents:

Bruksanvisning för bilstereo . Bruksanvisning for bilstereo . Instrukcja obsługi samochodowego odtwarzacza stereo . Operating Instructions for Car Stereo . 610-104 . SV . Bruksanvisning i original

10 tips och tricks för att lyckas med ert sap-projekt 20 SAPSANYTT 2/2015 De flesta projektledare känner säkert till Cobb’s paradox. Martin Cobb verkade som CIO för sekretariatet för Treasury Board of Canada 1995 då han ställde frågan

service i Norge och Finland drivs inom ramen för ett enskilt företag (NRK. 1 och Yleisradio), fin ns det i Sverige tre: Ett för tv (Sveriges Television , SVT ), ett för radio (Sveriges Radio , SR ) och ett för utbildnings program (Sveriges Utbildningsradio, UR, vilket till följd av sin begränsade storlek inte återfinns bland de 25 största

Hotell För hotell anges de tre klasserna A/B, C och D. Det betyder att den "normala" standarden C är acceptabel men att motiven för en högre standard är starka. Ljudklass C motsvarar de tidigare normkraven för hotell, ljudklass A/B motsvarar kraven för moderna hotell med hög standard och ljudklass D kan användas vid

LÄS NOGGRANT FÖLJANDE VILLKOR FÖR APPLE DEVELOPER PROGRAM LICENCE . Apple Developer Program License Agreement Syfte Du vill använda Apple-mjukvara (enligt definitionen nedan) för att utveckla en eller flera Applikationer (enligt definitionen nedan) för Apple-märkta produkter. . Applikationer som utvecklas för iOS-produkter, Apple .

och krav. Maskinerna skriver ut upp till fyra tum breda etiketter med direkt termoteknik och termotransferteknik och är lämpliga för en lång rad användningsområden på vertikala marknader. TD-seriens professionella etikettskrivare för . skrivbordet. Brothers nya avancerade 4-tums etikettskrivare för skrivbordet är effektiva och enkla att

Den kanadensiska språkvetaren Jim Cummins har visat i sin forskning från år 1979 att det kan ta 1 till 3 år för att lära sig ett vardagsspråk och mellan 5 till 7 år för att behärska ett akademiskt språk.4 Han införde två begrepp för att beskriva elevernas språkliga kompetens: BI

**Godkänd av MAN för upp till 120 000 km och Mercedes Benz, Volvo och Renault för upp till 100 000 km i enlighet med deras specifikationer. Faktiskt oljebyte beror på motortyp, körförhållanden, servicehistorik, OBD och bränslekvalitet. Se alltid tillverkarens instruktionsbok. Art.Nr. 159CAC Art.Nr. 159CAA Art.Nr. 159CAB Art.Nr. 217B1B