I recently had an ESD failure at 25KV in air with a network of 330pf 2oooR, Passed at 150pf 2000R
One of the components blow with was protected by a tvs diode PESD5VL1BA, this is spec'ed to >23kv. When I tested the tvs was fine but my analogue gate failed.
Is it possible that the tvs diode is not up to the job . I could replace it with a PESD5VS1BA which is spec'ed to >25kv.?
If a tvs diode gets a pulse too high will it not reduce the pulse correctly?

 

It would be a lot easier to answer your questions if we knew what you are doing. The details you gave us are without any context. Are you testing components or devices or is this a failure on some kind of installation?

 

If a tvs diode gets a pulse too high will it not reduce the pulse correctly?

Show us the schematic and include any other relevant details.

 

Show us the schematic and include any other relevant details.

 

I'm trying to protect u4 , but when an esd gun with a filter of 330pf 2k 25kv was put near it the chip blows. IF i use 15opf 2k filter the chip is protected

 

On the blown chip, what is damaged? The TVS diode is only protecting the chip from transients on Bus B.

 

Not too sure , the output voltage was incorrect though. The thing is that confusing me now is the Ipp rating The standard Ihave to work to is ISO 10605 .with filter at 150pf 2000r and 330pf 2000r it passes 150pf 2000r but fails 330pf 2000r. The tvs I have in at the moment has an IPP rating of 18v and esd protection of >23kv and The s version has esd protection of 30kv but Ipp is only 8A
When I look at the ISO spec if I'm reading it correctly the current is around 22A at 25kv.
Looking at tvs specs you can not get a 5v tvs with an Ipp greater than 18A

 

You still need to know how the device failed, Otherwise you may be trying to solve the wrong problem. If the input to Bus A or the supply failed, changing the TVS diode will not help. You need to test again with adequate protection on the supply and Bus A shorted to ground.