ESD Protection Guidelines

[imnavajas]

Hi all,

I would like to open a thread about ESD protection design guidelines. This topic comes up to me in order to have a CE complilant design, more precisely the IEC1000-4-x immunity specifications. In the end the theory is pretty clear, but once you have to implement it in one real design the doubts arise...

So, I wonder what kind of design guidelines you guys take into account in order to ESD protect, for example, digital I/Os, Analog I/Os, digital interfaces (USB, RS232,...), and when it should be applied given a certain set of I/Os.

Normally I protect digital inputs that interface with the 'outside world' of the board, (i.e., a digital input coming to the board from an alert situation of a machine being monitored) by means of a TSV diode in front of an optocoupler. What do you think about this topology? Another thing is knowing if the TSV diode has been chosen properly...

Thanks and hope you find this topic interesting.

[robertferanec]

Hi imnavajas, from my experience, very important part of ESD protection is Enclosure and Connectors. For example, when you have a metal enclosure and you use the right connectors which are properly touching the enclosure, it helps ESD a lot - often you are not able to touch the signal pins without discharging into the enclosure first.

To choose ESD componnents, I normally follow the reference schematic - they suggest the ESD protection. If you are not sure, try to find reference schematic with the interface you are using. To give a more specific example, you can have a look at our iMX6 REX Develoopment Baseboard and check what ESD protection components we used. I attached the schematic.

Also, normally I try to place the ESD components very close to the connector with direct and short tracks between pins (no VIAs used). I hope it helps.

[imnavajas]

Thanks Robert for your answer.

I've been watching the schematic and I wonder how do you decide which connectros are prone to be ESD protected, for example, in iMX6 REX Develoopment Baseboard I see USB's and SIM Card for PCI that are ESD protected, but GPIO's are not (the PCA9535BS I2C GPIO Expander is connected to male headers that maybe could be more likely to ESD sparks, and imagine that the PCA9535BS is not ESD protected for what I mean), I always think that this could be dangerous but I dont know if this is right.

I think that a solution for this copuld be the optocoupler to optoisolate not just different devices but also ESD transients, but I dont know if this kind of devices are ESD immune by itself or should be protected too by TVS diodes. As always, it dependes where you read..

Thanks!

[robertferanec]

Generally, if connections stay inside the enclosure, the on chip ESD protection should be fine. If it goes out, you need to protect it.

BTW, what video are you referring to?

[imnavajas]

Sorry, I meant the PDF schematic that you attach, not that I watched any video!

[robertferanec]

Ah, ok I thought you were watching a video with schematic