Is TVS Protection permanent?

Tip / Sign in to post questions, reply, level up, and achieve exciting badges. Know more

cross mob
Not applicable
How many ESD strikes does a Silicon based TVS diode withstand?
0 Likes
4 Replies
Alexander_Glas
Employee
Employee
Hello SWhiley

There is NO performance degradation of a silicon based TVS diode after a high number of ESD zaps.
It is clear that the applied ESD zaps must not exceed the stated ESD level.
There is no difference to zap on a silicon based TVS diode 10 times or stress with several thousands zaps.
This is the big advantage of silicon based TVS diodes compared to other non silicon based protection devices.
0 Likes
Not applicable
Thank you Alexander.

We are using the IEC61000-4-2 testing standard. In some occasions we observe an increase in the first peak overshoot. At the beginning we thought it was certain degradation but now we realize it is more likely due to layout issues. Is there any recommendation in regards to the layout requirements in order to ensure a proper working of the protection device?
0 Likes
Alexander_Glas
Employee
Employee
Hi SWhiley,

there are different contributors being responsible for the first peak overshoot.
The peak overshoot happens at the moment the ESD gun current rising speed in a maximum, just before the gun current reaches his maximum amplitude.
Furthermore this event happens in the very early phase of the gun strike.
The TVS diode must move from an isolating state in conducting state. During this very short transient time the TVS diode does not provide his final low ON resistance (dynamic resistance).
This kind of delay results into a certain amount of peak clamping voltage.
This transient time bases on TVS diode characteristic, but is normally << 300ps

An other contributor is the internal bond wire AND external serial inductances, caused by the layout.
As mentioned before there is a huge ESD current rising speed visible at the beginning of the gun strike.
A clamping voltage overshoot is generated proportional the rising speed of the ESD current (dI/dt) times the serial inductivity.
The device internal serial inductivity (bond wire) is quite small. For TSSLP (0201) ~0.2nH, for TSLP (0402) ~0.4nH, for Chip Scale Package there is NO bondwire anymore.
The designer can influence the total amount of serial inductivity, generating a good PCB layout.

This means:
• The TVS diode should be placed direct on the “protected” signal line without any serial stub line.
If the TVS diode should be relocated from the signal line, signal line has to be bended (like a “Y) to connect the TVS diode without stub line
• GND node of the TVS diode must be fed direct to system GND without any serial stub line.
Taking this layout rules into account, first peak overshoot can be minimized.
0 Likes
Not applicable
Alexander,

thank you very much for your quick reply with suggestions. I will take a look on the items you mentioned.
Another issue facing right now is lack of reproducibility with the air discharge testing so we are trying to get this fixed too.
your recommendations are welcome.
0 Likes