ESD / General Protection of Communication Lines

Hi all,

You may have seen a few threads of mine recently asking about general protection methods for GP I/O lines, from ESD.

However, I've also got USB, RS232 and CAN all brought out on headers - which of course connect up to some wiring, so how would one go about protecting these pins from ESD - as clearly adding capacitance is going to destroy signal integrity. It seems there are specific diodes available for this purpose, but what are the general techniques?

Also, what about protecting such pins from things like shorts to ground, VCC or to eachother? I.e shorting USB signals to power? Perhaps this won't be of harm itself if the device can withstand the voltage, but then a voltage spike on an unregulated power line may destroy the protection?

I'm trying to make my device as robust as possible, protected not only against ESD but any form of damage to the wiring between devices that could result in shorts between pins, to ground etc. I know perhaps wanting to protect a pin from transients in the rare chance they are shorted to a power rail is an unusual require, but it's what I want to achieve.

Many thanks in advance.

Littelfuse has lots of docs in its technical resources section. Here's a good starter:

The protection of the Arduino pins can have several techniques. The LittleFuse document is a good starting point, as Chagrin has written. In addition, you can take the following actions :

1 Buffer ICs The pins from Arduino can go to additional ICs called Buffers. This will isolate the core product with an expendable boundary. Sockets for the Buffers will allow any damaged Buffers to be replaced with another identical, cheap Buffer. The Buffers are bi-directional for input and output communications directions. The Buffers will be robust bipolar devices with no CMOS gate oxides to be destroyed.

2 Resistors It is safe to connect series Resistors as the first connection point of vulnerable signals. The value of each Resistor can be from 1 ohm to 10k ohms, depending on the pin specs. Short circuited power supplies will encounter the Resistor so that the current is limited to a known values. If an 8000 volts ESD event hits the Resistor and a diode is next in line, the diode will not be subjected to the full 8000 volts.

3 Diodes to capacitors and relays An ESD protection diode can be connected to a series capacitor instead of being connected to a rail. Then, the capacitor can temporarily absorb the excessively high voltage, giving time for a relay to disconnect ground and Vcc during the event. The first microseconds during the over-voltage event will cause the diode to forward bias, the capacitor charges up, relays are opened so the power rails float. Then the entire Arduino product can have its common mode voltage rise to the over-voltage level, preventing any voltage differential from appearing across two nodes. The advantage is that no components get ruined by a powerful surge of a voltage while the Arduino communications signal is isolated from any protective capacitance and resistance that could have degraded signal integrity.

Transorbs are good for protecting comm lines, where you don't want too much capacitance loading. They are similar to zeners, but much lower inductance, so they react fast to transients.