Opamp ESD protection

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Wondering what techniques people use for protecting analog signals against transients.. diodes don't work so well on small signals.

Right now I'm using a ceramic cap / series resistor model that works OK, in combination with some ESD protected LM324K opamps. Would like something a little more robust, however.

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xtal wrote:
.. diodes don't work so well on small signals.

The leackage current of signal diodes becomes a problem if you place them after the opamp's input resistors. However, you can alleviate this problem by splitting the input resistors into 2 in series and place the diodes after the first resistor. Use of low leackage diodes will also help.

I wonder if a matched pair of signal diodes in the same package would have better differential leakage. Its the net injected current that will add to offset.

Using opamp stages with G<1 effectivly multiplies the input common mode tolerance of the opamp stage.

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There are low leakage diodes so they don´t change your analogue signal.

leakage current changes with voltage across the diode. So one technique is to have equal voltages at both diodes (with additional opam and other circuitry. Or (even better) to make something lieke "aktive shielding" or "guarding" where you create a voltage with exactely the same voltage as your input and use this voltage to protect the inputs. So with ususal signal frequencies the voltage will vollow your input and zero voltage is across your protecting diodes (no voltage - no current). But with the very fast transients the diodes get conducting. Usually you need R C and additional protecting diodes.

Klaus
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