Design News, February 2013

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Design Decisions The Secret to Eliminating ESD Damage? Read Your Datasheet If you don't carefully examine your datasheet, the results can be disastrous. Don't assume you know what something means, experts say. by Charles j. murray, seNIOr TeChNICal eDITOr, eleCTrONICs & TesT Ipeak I 100% 90% I at 30ns I at 60ns 10ns 30ns 60ns tr = 0.7 to 1ns t A typical IEC 61000-4-2 ESD waveform is characterized by its subnanosecond rise time and its short (~100 ns) duration. datasheet," Marak said. "But if you don't read the fine print underneath that plot, you as a designer could be misled.That plot may not apply to your device." The chances of overlooking critical information are accentuated by the fact that many designers are juggling multiple projects, and therefore believe they don't have the time to comb through every word on the sheet. But by reading the fine print, Marak believes that designers might actually save time. Know your standards. There are two different standards for ESD design. One, the so-called Human Body Model, applies to manufacturing environments.The other, the International Electrotechnical Commission's IEC 61000-4-2, applies to handheld devices, such as portable phones and computers. Design News | february 2013 | www.d esign n –16– Source:Littelfuse Inc. The scourge of electronic devices — electrostatic discharge (ESD) — can be virtually eliminated by designers doing one simple task: reading their datasheets. Experts advise to read them slowly, carefully, and all the way down to the fine print. Don't overlook a single word, they say. The result could be the elimination of functional failure, shock or even fire in an electronic device. "Sometimes designers move too fast and assume they know what something means," Chad Marak, director of technical marketing for Littelfuse Inc., told Design News recently."But without reading all the way down to the fine print, they may find out that the information on that datasheet doesn't mean what they think it means." Unfortunately, there's no way to quantify the relationship between careful scrutiny of a datasheet and flawless ESD performance. But it exists in devices ranging from televisions and smartphones to MP3 players and blood pressure pumps, Marak said. The trick is to know and understand the relevant specs, thus making the datasheet more understandable. Equally important, designers need to respect and understand the potential damage caused by the enormous voltages and currents that can strike an electronic device, if even for a few nanoseconds. "Walking across a carpet in winter, when the humidity level is low, and picking up a piece of electronic equipment, you can easily inject 15,000 volts," Marak told us. "It can be about 30 amps. Most people would consider that substantial, even though it lasts for only about 100 nanoseconds, which is much less than the blink of an eye." Marak suggests the following for designers who are concerned about the effects of ESD. Read the fine print. The ESD plot on the datasheet may not apply to your design, but you won't know that without careful scrutiny."Manufacturers will inject an ESD pulse into the device they're selling, and then show a plot of it on the

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