Varistor clamping voltage calculation for ESD

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ku637

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Hi,

I would like to know if it is possible to calculate the clamping voltage provided by a varistor to an IC pin for an automotive ESD waveform ISO-10605 8kV.

I would like to know if it will protect my circuit?

example datasheet https://industrial.panasonic.com/cdbs/www-data/pdf/AWC0000/AWC0000C52.pdf

Thanks,

- - - Updated - - -

Sorry for the double post..i got a message like the first post is closed. Thats y mistakenly i tried to repost
 

Thanks..Yep sorry my mistake, I know the clamping voltage is specified there, what i really wanted was the peak current calculation for that particular waveform.. and since it is a non linear impedance.. im not sure the like in TVS dynamic resistance can be used here.. I want to make sure that my varistor is rightly sized for the application.

Any suggestions welcome
 

Without an additional series element, a varistor between IC pin and ground will probably not increase the ESD strength much.
 
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    ku637

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Fvm, Thanks for the input, But ESD generator has a built in resistor right (330Ohm typical), or are you mentioning we need to put additional resistors in the line being protected.
Im intending to use it in CAN bus interfaces, im not sure if i can add series resistors there..
 

Hi,

Now you said ESD voltage and you know the series resistance....thus you can calculate the peak current.
Then from the V-I chart you can see the peak clamping voltage.
I assume this value is way above what you expected.
Now with an additional series R between Varistor and IC you can limit the IC input current.

Klaus
 

ESD generator impedance limits the discharge current to several 10 A, can you show that the varistor clamps the pin voltage to a safe level at this current? I presume you can't.

A varistor can play a role in a staggered protection scheme, but you most likely need a series resistor or inductor between external clamp and IC pin.

Alternatively an ESD diode with steeper clamp characteristic than a varistor can provide effective protection.
 
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