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DadOf3TeenieBoppers
I have seen 74AC logic turn into miniature volcanoes with a hole in the middle ...
Sanjib.Acharya
In general, the most vulnerable parts of the handheld devices through which ESD ...
Circuit protection can't be an afterthought
Charles Murray
8/20/2012 11:55 AM EDT
Understanding the environment
Don't wait too long. Colby told us:
The best time to start thinking about such matters is after you've picked out the chip set and begun laying out the circuit board, Colby said. Doing it in that way, ESD ratings are available and designers know how robust or how sensitive the chips are. "Some of these chips are running at 1.5 volts and you don't have to do a lot to upset them," Capdevielle said. "The circuitry is more complicated and more sensitive than we sometimes realize."
Understand failure modes. "Everybody understands a fuse, but over-voltage may not be so obvious, and people might not realize the consequences," Capdevielle said. The consequences, however, do exist, even if they are not as catastrophic as those of over-current. Over-voltage has incapacitated the Hubbell Telescope, shut down refineries, killed smartphones, and stopped roller coasters mid-ride. In some portable medical devices, over-voltages can even be life threatening, according to Capdevielle.
Sources of excessive current and voltage include lightning, ESD, motors, arc welders, and the aforementioned running shoes and hosiery, among others. "People understand lightning but they may not know it travels across the ground," Capdevielle said. "It can create huge glitches in power lines a mile away."
Define the threats. To accurately predict a product's circuit protection needs, the design engineer must first be able to imagine how it will be used. "You have to know where the product might end up," Capdevielle said. "You have to understand its environment and what might be adjacent to it. A device will be more susceptible to a factory setting than to an office."
Once the designer understands the environment, he or she can begin making accommodations. "You should start with the connection points," Capdevielle said. "You should have an over-voltage device, not three inches away, but as close as possible to the connector."
Next: Where to find help
Don't wait too long. Colby told us:
- Circuit protection can bite you if you do it too late in the project. You could put yourself in a situation where the space is not available for your ESD device. You end up settling for a non-optimal location, where the device won't function the way it's supposed to.
The best time to start thinking about such matters is after you've picked out the chip set and begun laying out the circuit board, Colby said. Doing it in that way, ESD ratings are available and designers know how robust or how sensitive the chips are. "Some of these chips are running at 1.5 volts and you don't have to do a lot to upset them," Capdevielle said. "The circuitry is more complicated and more sensitive than we sometimes realize."
Understand failure modes. "Everybody understands a fuse, but over-voltage may not be so obvious, and people might not realize the consequences," Capdevielle said. The consequences, however, do exist, even if they are not as catastrophic as those of over-current. Over-voltage has incapacitated the Hubbell Telescope, shut down refineries, killed smartphones, and stopped roller coasters mid-ride. In some portable medical devices, over-voltages can even be life threatening, according to Capdevielle.
Sources of excessive current and voltage include lightning, ESD, motors, arc welders, and the aforementioned running shoes and hosiery, among others. "People understand lightning but they may not know it travels across the ground," Capdevielle said. "It can create huge glitches in power lines a mile away."
Define the threats. To accurately predict a product's circuit protection needs, the design engineer must first be able to imagine how it will be used. "You have to know where the product might end up," Capdevielle said. "You have to understand its environment and what might be adjacent to it. A device will be more susceptible to a factory setting than to an office."
Once the designer understands the environment, he or she can begin making accommodations. "You should start with the connection points," Capdevielle said. "You should have an over-voltage device, not three inches away, but as close as possible to the connector."
Next: Where to find help
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kinnar
8/20/2012 4:03 PM EDT
ESD is more problematic in the cold and dry areas, on equatorial plane it is not that much problem creating. But still protection is must, self resetting fuses are great designs. This too requires proper selection in a way the fuses it self does not get damaged that it could not reset.
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Michael J.
8/20/2012 4:31 PM EDT
Any good ESD protection device will offer more than just protection from super high voltage discharge.
A breakdown voltage slightly outside the signal voltage range also prevent from damage of transients.
A combination of ESD protection and e.g. EMI-filtering also reduces the cost adder for the ESD only function.
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ReneCardenas
8/21/2012 11:28 AM EDT
It may not be thaught in college but it is among the first lessons learned after a poorly under-rated fuse is spec'd, and the rush currents get closer scrutiny in all those odd cases that nobody thought were possible.
Yeap, most EE experience that in at least the first project, I agree since most testing is limited by time2market constraints.
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Brutus_II
8/21/2012 12:08 PM EDT
To take it a step further, ESD and EMI protection can be combined as a single step (EMI from EMP generated from such nasty things as weapon detonation very high in the atmosphere at say, the center of the U.S.). The fix is simple and relatively inexpensive. Yet in a such a competitive industry where every last mil (1/10 cent) counts, such things are not usually considered save for military and a few other critical applications. Our cars and PC's are not considered critical, unfortunately.
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DrQuine
8/22/2012 12:10 AM EDT
Regardless of the tremendous number of opportunities for static electricity to damage portable electronic devices, such events seem to be rare. We've all walked across a rug on a dry winter day and experienced a shock when we touched a conductive surface ... Is it because of exceptional circuit design or is it simply that the outer case of the devices serves as a Faraday cage and protects the contents that we rarely experience catastrophic events for our handheld devices under such circumstances?
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Sanjib.Acharya
8/26/2012 5:34 AM EDT
In general, the most vulnerable parts of the handheld devices through which ESD could cause damage are the ports (such as USB) exposed to the user. Proper protection is needed for the ports.
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DadOf3TeenieBoppers
8/27/2012 10:56 AM EDT
I have seen 74AC logic turn into miniature volcanoes with a hole in the middle of the package, bond wires strung out in the air, and all of the silicon vaporized when someone wearing a nylon shirt rubbed up against the board one day. The poor guy nearly jumped out of his skin when it happened.
Static happens. Plan for it. An ounce of prevention is worth a pound of cure.
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