Selection of ESD diodes

[FreshmanNewbie]

My objective is to protect the pins of a device.

The pins are connected to an external connector which might be exposed to an ESD event.

Hence, I need to place an ESD protection device on that line.

So, my understanding is that, suppose, let me assume that the pin I am trying to protect is a USB signal from a USB hub which is going to a USB connector.

What I do is, search for a diode. The only parameter that I look for is the clamping voltage of the diode. Since the USB signal voltages during normal operation don't go beyond 4V, I select a diode that has a clamping voltage of 5V (max) @ 1A. And I make sure this clamping voltage of 5V doesn't exceed the absolute maximum ratings of the device's pin in the Hub, which is 5.5V.

Is my approach correct? If not please tell me what is wrong.

Also, please let me know if I have to consider additional paramters while selecting an ESD diode to protect the pin of a device in general.

Thanks.

 

[KlausST]

Hi,

if you want to protect USB from ESD damage ... What keeps you from doing a search (distributor, semiconductor manufacturer, internet ..) for "USB ESD protection"?

You will find documents with very informative and detailed content, and you will find schematics, you will find suitable parts, you will find standards for ESD pulses...

I mean: USB isn´t USB, ESD pulse isn´t ESD pulse. There are very different types of both.

Klaus

 

[FreshmanNewbie]

Hi,

if you want to protect USB from ESD damage ... What keeps you from doing a search (distributor, semiconductor manufacturer, internet ..) for "USB ESD protection"?

You will find documents with very informative and detailed content, and you will find schematics, you will find suitable parts, you will find standards for ESD pulses...

I mean: USB isn´t USB, ESD pulse isn´t ESD pulse. There are very different types of both.

Klaus

Yes, can you tell me whether my approach for finding the right clamping voltage is correct?

 

[FvM]

ESD pulse currents are in a range of several A to several 10 A, depending on the discharge model. I know that you have already reviewed many ESD diode datasheets, you posted some of it in your various ESD related threads. So I presume you didn't miss the fact that actual clamping voltages at typical ESD currents are considerably higher than maximum rating e.g. of USB interface devices. ESD diodes still serve a purpose because interface devices are also provided with internal ESD protection, but with limited energy handling. In a combination with external ESD protection, a larger part of discharge energy is absorbed externally and the remaining overvoltage internally handled.

For fast signals, ESD diode capacitance is an important parameter, using large capacitance protection diodes, e.g. power TVS diodes would kill your signals.

 

[KlausST]

Hi,

You don´t protect USB from damage, you protect an IC from damage.

Basically every IC comes with a datasheet. So does your USB device (sadly we have no link to the datsheet nor the exact name).
Within this datasheet there is a paragraph "absolute maximum ratings". This tells you what maximum voltage may be applied to the according pins.

But for sure this is not everything that matters. What does a good protection level help, if it violates proper USB communication.
* Diode capacitance - for example - matters.
* And why 1A? Just guessed?

But all this stuff is well documented. Usually the IC manufacturer provides additional infromations regarding ESD protection, maybe even desgin notes, example schematics, example protection devices, example evaluation boards.
The documents also tell you that choosing a suitable protection device is only half the way. Choosing the best protection diode, but not using a low impedance GND plane is simply useless - it may result in "no protection".

This is where I have the knowledge from. Reading documents is how professionals do it. And therefore I recommend the same for you.

Klaus