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William Murray

ESD Protection for Analog Circuits

William Murray
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Hughston
Hughston
8/26/2013 10:46:08 AM
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Newbie
Re: ESD Protection
A good question my friend.  I think ESD is trying to go to power or ground. If you have a wired connection to outside the box or system; ESD wants to go out on that wire and you get a higher current if your system is wired to the outside world rather than isolated. If you test a hand held battery powered device that is not hooked to a charger, that is an easy device to protect because the current won't be high unless it has somewhere to jump to through the device. Like for example, if you test the device on a metal table instead of a insolated table. You want ESD protection devices to take you to the system power, ground or a big cap as soon as possible. If you have an ESD protection device at an interface port, put a large cap on its power to ground connection. On thing you'll notice on some of these external interface ports is longer ground connections. That has a dual purpose. You want to make the ground connection first for electrical reasons, but you also want ESD hits to go to ground.

Sometimes a capacitor is good protection for ESD against induced failures. The capacitor can act as a high frequency filter for induced voltages. This technique was used for resistive touchscreens and MOSFET gates.

To answer your question about the voltage gradient, you want to get the ESD current to the system single point ground for the power. You have the biggest cap there and it keeps the ESD from getting there through a processor or other sensitive chip. Here is another point: if you have an isolated wall wart, the ESD will blow right through it. After many hits the insulation breaks down and the current keeps increasing and makes the system more sensitive.

One advantage engineers have today is that chips have much better ESD immunity than back in the 80s when these problems started getting noticed. Back then you had to try different vendors for ESD immunity. Today with chips so specialized, you wouldn't have than luxury.

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B_Albing
B_Albing
8/23/2013 4:12:04 PM
User Rank
Editor
Re: ESD Protection
@Hughston - you're hitting on an important consideration - where does the current flow from/to during an ESD event. And what effect does that have regarding inducing voltage gradients and current flows in nearby conductors.

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B_Albing
B_Albing
8/23/2013 4:09:15 PM
User Rank
Editor
Re: ESD Protection
@samicksha - depends on where the charge is accumulated. More to the point, if you have an IC with that many pins, you'd need to add lots of ESD protection to all of them. But maybe not all would need the same amount of protection. Peak voltage and current levels may vary.

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B_Albing
B_Albing
8/23/2013 4:05:40 PM
User Rank
Editor
Re: ESD Protection
@DaeJ - I think there are detailed protocols and test techniques set out in the various standards that describe precisely how these ESD tests are to be performed.

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Hughston
Hughston
8/15/2013 10:42:48 AM
User Rank
Newbie
Re: ESD Protection
The most important basic step is good physical isolation of the electronics and good EMI design. Use insulating materials in the mechanical design to increase isolation.  Insulate around displays, keypads and buttons especially. Beware of ESD strikes jumping through metal or through air holes in the enclosure to the PCB.  Another important step is pay attention to your reset circuit.  Avoid long traces. Use an ESD guard trace around the perimeter of the PCB, but this can cause induced failures. MOVs are not as good as transzorbs and low capacitance protection devices for lightning and ESD. Beware of excess lead length if you have leaded components. ESD can jump to a lead. Keep traces away from the perimeter of the PCB and round pads and traces near the perimeter.

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samicksha
samicksha
8/14/2013 4:38:39 AM
User Rank
Artist
Re: ESD Protection
I am curious understand about design challenge. As the average pin count for modern ICs increases to above 3000 pins, the total stored charge increases, which translates into a significantly increased peak ESD current.

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Netcrawl
Netcrawl
8/13/2013 10:26:57 AM
User Rank
Master
Re: ESD Protection
Thanks for a great article, as IC process-technology nodes continue to evolve and get smaller, they become increasingly more susceptible To ESD damage, not just in manufacturing process but also in the real-world environment. 

Gadgets like smartphones, laptop and computers introduce could introduce a more severe level of ESD, its is important to know that survival through the manufacturing process does not guarantee survival in the real-world environment, an ESD protection like ESD supressors, may be ncessary its a good idea to have this. 

 

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DaeJ
DaeJ
8/12/2013 10:03:03 PM
User Rank
Master
Re: ESD Protection
ESD Gun which set 0.5KV to 30KV might use for ESD testing. High voltage could be programmed in the tool.  Be carefully for using ESD Gun not to touch board by hand while shooting the device by Gun.

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samicksha
samicksha
8/12/2013 2:35:28 PM
User Rank
Artist
Re: ESD Protection
I guess most common example of a natural spark is lightning, wherein the electric potential between a cloud and ground, or between two clouds, is typically hundreds of millions of volts, also not to miss due to it gets more complicated when we look at the concern that dielectric nature of electronics component and assemblies, electrostatic charging can not be completely prevented during handling of devices.

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