Chuck Murray tells why electrostatic discharge can be a scourge if you don't read down to the fine print on your datasheet.
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., said in an interview. "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."
A typical IEC 61000-4-2 ESD waveform is characterized by its sub-nanosecond rise time and its short (~100 ns) duration.
(Source: Littelfuse Inc.)
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.
Marak told us:
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. 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. Marak said:
Manufacturers will inject an ESD pulse into the device they're selling, and then show a plot of it on the datasheet. 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.
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. "You need to know, is the datasheet showing an IEC pulse or an HBM pulse?" Marak said. "It makes a big difference."
Is it applicable? Many protection device datasheets call out 2kV and 4kV pulses, even though the majority of product manufacturers use 8kV as a benchmark. "If I'm using 8kV, then I don't care what a 2kV plot looks like," Marak said.
Know how datasheet clamping voltages are measured. Make sure the clamping voltages referenced in the datasheet correspond to your design. "If they're stating a clamping voltage between pins one and two, then make sure you're connecting to the same pins in your circuit," Marak said.
Use the right layout. "Even if you've purchased the best circuit protection device in the world, it won't matter unless you use the proper printed circuit board layout," Marak said.
For designers, the bottom line is vigilance and experience. Experienced designers typically are better at understanding the subtleties of datasheets, but even the best can be fooled if they don't examine the sheets closely. Marak said:
Manufacturers use creative marketing to present their devices in the best light. So if you don't take the time to read the datasheets and understand the ESD characteristics, then you could mislead yourself into buying a device that's not going to give you the protection you expect.
To learn more about Littelfuse's Speed2Design site, click on the link.