Tip Number 22
Place ESD protection as close as possible to the connectors.
This is what I mean.
On the board there are some components to protect it.
Yeah, like this one.
And this one.
What is the ESD? Electrostatic Discharge? Do you know?
I'm pretty sure it happened to everyone.
When you are trying to touch something, there is a spark between your finger and the thing which you would like to touch.
Or you know between your finger and the other person or it very often happens between people.
This spark...
This ESD, electrostatic discharge, it can damage electronics.
It can damage your board, it can damage some peripherals, it can damage some chips.
So you would like to protect your board.
You would like to protect the places
or the signals where this ESD
could possibly go inside your board.
So you use this kind of components, and it is very...
Important how you place these components.
Usually the components they are diodes
and
you know based on data sheet you can see what is the voltage when this diode is going to clamp
the signal which is on the diode basically...
It's going to...
Discharge... The very high voltage pulse is going to discharge it to the ground through this diode or to power rail.
Why it is important where we place these components, do you know?
When I was doing some tests I played with ESD gun.
It looks like this.
It's kind of fun.
And...
When I try to apply these...
Pulse...
Somewhere inside the board I could clearly see that it actually can discharge basically anywhere, yeah?
It travels...
Though the track and then it discharged for example to ground...
Which is very close to the signal...
Or it can discharge to via, which is very close to the signal.
Or it travels inside the chip and it discharged inside the chip.
So when you are placing this protection you really don't want these high voltage pulse travel through your board.
Because you don't know where it is going to discharge.
It may discharge in the protection circuit, yeah?
But it may discharge anywhere on the way from the connector to the protection circuit.
So what you really would like to do...
You would like to place this protection circuit as close as possible to the connector.
That's what you can see here on these examples, yeah?
This is USB connector and the protection is placed immediately after the connector pins, yeah?
Also here.
Here are the pins from the connector and the signals they immediately go into the ESD protection.
So the pulse, possible pulse, which would be going inside the board through this USB connector...
It discharged immediately...
After it enters into the board it discharged here.
There is no other way or other place where it will discharge.
You don't want to place this protection somewhere here because then you don't know where it is going to discharge.
I'm pretty sure you understand
There are some other interfaces, which you would like to protect.
HDMI is a nice example
This one.
This is HDMI connector and here you can see the HDMI ESD protection circuit.
Again placed very close to the pins from the connector.
So don't forget
Tip Number 22: Place ESD protection as close as possible to the connectors.
Why?
So the ESD pulse doesn't travel through your board, and it discharges immediately behind the connector.