AN898/1100 1/4 AN898 application note emc general information by microcontroller division applications introduction because many electronic circuits are in proximity to each other, it is essential that their design is not affected by external noise sources and that the circuit itself is not a noise source af- fecting other circuits. this relationship is known as electromagnetic compatibility or emc . sources of electromagnetic noise are numerous and have both natural and man-made ori- gins. natural sources below 10 mhz are dominated by the atmospheric noise generated by elec- trical storms. above 10 mhz, natural sources consist primarily of cosmic noise and solar radi- ation. man-made noise include am, fm, tv and other broadcast transmitters, mobiles radios but also computing devices, motors, appliances, power lines, auto ignition systems and many others. with the proliferation of these sources (particularly in urban areas), electromagnetic noise has reached important levels. for detailed information regarding emc guidelines for microcontroller - based applications, please refer to an901. figure 1. electromagnetic radiation sources natural origin man-made origin electromagnetic radiation vr02102a 1
2/4 emc general information 1 emi and ems almost every electronic device emits some electromagnetic interference (emi) . these emissions can be transmitted as electromagnetic radiation or conducted through cables such as power cords. at the same time, most electronic devices are susceptible to emissions generated either internally or by other devices. receptors susceptible to electromagnetic radiation include communication receivers such as radio and television, radar and navigation devices or computing devices. the effect of the in- terference on the receptor depends on several parameters: strength of the source, transmis- sion medium, distance from the source, coupling mechanisms and degree of susceptibility of the medium. figure 2. emc contents: emi and ems electromagnetic interference (emi) tests involve measuring the frequency and amplitude of undesirable signals emitted by the tested equipment. signal radiated into free space are called radiated emissions , whereas signals travelling along power cords or other intercon- necting cables are called conducted emissions . electromagnetic susceptibility (ems) testing is a way to determine the ability of the device to operate properly in an undesirable electromagnetic environment. these tests use signal sources and power amplifiers to generate high level fields around a device. conducted sus- ceptibility measurements are performed by coupling an offending signal of a specified level onto cables to try to induce a malfunction into the tested device. other forms of susceptibility tests include electrostatic discharge (esd), transient burst and voltage surge testing. vr02102b electromagnetic susceptibility ems emi electromagnetic interference radiated conducted radiated conducted emc electromagnetic compatibility 2
3/4 emc general information 2 emc regulations regulations are one of the primary reasons we test products for emc. therefore, we will now look at some of the important organizations that develop and enforce emc regulations. failing to comply with emc regulations can result in forced removal of a product from the market place or even monetary fines. figure 3. conducted versus radiated regulations emc regulations cover the entire spectrum of electrical products, from computing equipment to microwave ovens to aircraft. as shown, the frequency ranges of interest for emc testing ex- tend from 30 hz to 40 ghz (9 orders of magnitude), depending on the agency and the type of measurement. the frequency range over which regulations exist varies, depending on the de- vice and its intended use. while individual emc requirements vary widely from one another, one common aspect is the goal of achieving valid, repeatable results. therefore, most regulations specify the test envi- ronment, receiver and transducer characteristics. antenna height and polarization is usually varied, and the tested equipment is rotated to find the maximum response from the device. all these actions help insure that the worst-case emissions are found. because so many factors affect emissions, an environment with known characteristics must be used when measuring electromagnetic interference. testing within a known environment is critical in order to assure meaningful and repeatable results that can be compared to other measurements performed on other devices. vr02102c mil- std 30 hz 40 ghz en 9khz 1ghz fcc 30 mhz 40 ghz mil-std 450 khz 30 mhz 30 mhz 9khz en fcc fcc federal communications commission en european norms mil-std us military norms frequency (herz) conducted radiated 1hz 1khz 1mhz 1ghz 30 hz 40 ghz
4/4 emc general information athe present note which is for guidance only aims at providing customers with information regarding their products in order for them to save time. as a result, stmicroelectronics shall not be held liable for any direct, indirect or consequential damages with respect to any claims arising from the content of such a note and/or the use made by customers of the information contained herein in connexion with their products.o information furnished is believed to be accurate and reliable. however, stmicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of stmicroelectronics. specifications mentioned in this publication are subject to change without notice. this publication supersedes and replaces all information previously supplied. stmicroelectronics products are not authorized for use as critical components in life support devices or systems without the express written approval of stmicroelectronics. the st logo is a registered trademark of stmicroelectronics ? 2000 stmicroelectronics - all rights reserved. purchase of i 2 c components by stmicroelectronics conveys a license under the philips i 2 c patent. rights to use these components in an i 2 c system is granted provided that the system conforms to the i 2 c standard specification as defined by philips. stmicroelectronics group of companies australia - brazil - china - finland - france - germany - hong kong - india - italy - japan - malaysia - malta - morocco - singapore - spain sweden - switzerland - united kingdom - u.s.a. http:// www.st.com
|
