[SOLVED] Selection of resistor& Capacitor in ESD protection circuit - IEC61000-4-2 standard

[jebaspaul]

Selection of resistor& Capacitor in ESD protection circuit - IEC61000-4-2 standard

Hi,

I am designing a Data acquisition system. The input of this system should provide ESD protection according to IEC61000-4-2 standard. My input section is as shown in figure. I am not afford to use Transorb(TVS diodes) at the input, because of its leakage current. Since my system resolution is 16 bit and source resistance is 500 ohm, even a 1uA of leakage current reduces the signal amplitude by more than a LSB.
Because of the above said limitation, I am using a simple RC network for ESD protection. According to the IEC61000-4-2 standard the peak voltage is +/-4KV and total period of pulse is 70ns. So, the Power dissipated by the resistor is calculated as;

P(resistor) = (4K)^2/R = 1.6 KW ; if R = 10Kohm

So, the resistor should support a pulse load of 2KW and a pulse voltage of +/4KV for a time period of 70ns.
The capacitor should support a peak current of 1A and a pulse voltage of +/4KV for a time period of 70ns.

I couldn't find the appropriate resistor and Capacitor for this rating. Can anybody suggest some parts which satisfies this specification.




Thanks,
Jebas.

 

[GUMY]

Re: Selection of resistor& Capacitor in ESD protection circuit - IEC61000-4-2 standar

Use low leakage TVS (like PESD5ZXX). Use higher voltage TVS than Your input signal rating, this will push leakage current in pA region. Remaining overvoltage (in range of 10-20V) is easy ro handle with RC network.

 

[emresel]

Re: Selection of resistor& Capacitor in ESD protection circuit - IEC61000-4-2 standar

What is the bandwidth of your input signal. Keep in mind this is also a low pass filter. High freq signal will be filtered out.
You can use smd805 resistors for that purpose i think, since duration is very short. (after applying ESD sparks many times, resistor values might increase, i have experienced some cases like that, on the other hand for smd402 components are not proper, ESD spark may bypass the resistor since conducting terminals are too close).
By the way you can consider ferrite beads instead of resistors.

Good luck

 

[chuckey]

Re: Selection of resistor& Capacitor in ESD protection circuit - IEC61000-4-2 standar

I believe that you have to clamp the input voltage right at the input connector. Putting a series resistor in and letting the input connector to go to the 4KV, is stressing the connector beyond any reasonable levels. I would aim for a maximum of 100 ohms to limit the current into a pair of clamping diodes connected to 0V and +Vcc and maintaining the input connector to under 300V peak.
Frank

 

[jebaspaul]

Re: Selection of resistor& Capacitor in ESD protection circuit - IEC61000-4-2 standar

Thanks GUMY, emresel & chuckey.

The suggestions are very much useful for me.

I want to share the following link from where I got more information about selecting a appropriate component for ESD protection.

https://www.littelfuse.com/technical-resources/education-center/esd-suppression-solutions.aspx

Under this link there are two documenst which I found useful are;
1. Selecting an ESD Protection Device (PDF)
2. Tips for Enhancing ESD Protection (PDF)

Thanks,
Jebas.