Re: ESD protection as easy as a cheap LC filter?

From: Bill Sloman (bill.sloman_at_ieee.org)
Date: 07/08/04 

Date: 8 Jul 2004 02:11:50 -0700

"John Jardine" <john@jjdesigns.fsnet.co.uk> wrote in message news:<cchv7i$s3t$1@newsg1.svr.pol.co.uk>...
> Mike V. <valemike@yahoo.com> wrote in message
> news:8188616d.0407071245.4fefa5f2@posting.google.com...
> > There are a few ICs out there that protect against ESD (e.g. Maxim
> > MAX6818, a few ST transil parts, etc.).
> >
> > However, a while back, I was working at a place where the test house
> > passed our product against ESD after recommending a simple LC circuit:
> >
> > +5V
> > ___
> > |
> > <
> > <
> > input signal Inductor R |
> > ----------+-----uuuuu------^^^^---+------------>to micro's I/O pin
> > --+ |
> > | |
> > | ___
> > ---- C___
> > Gnd -- |
> > - |
> > ---
> > Earth Gnd///
> >
> >
> > Supposedly it works like this: When there is an ESD spike, the
> > inductor is momentarily an open circuit, and the capacitor is
> > momentarily a short to earth ground.
> >
> > For those of you familiar with ESD protection circuits, would you
> > think that this simple LC type of filter is sufficient against ESD?
> > Thanks,
> > Mike
>
> From experience I'm wary of LC's as input protection. There's potential for
> 'ringing' with particular transient signals.
> Depending on the particular circuit arrangement, the LC's can ring in // or
> series and serious attention needs paying to the damping components.
> Sometimes though the working impedance levels are so low that that L's are
> the only real bet.
> Yes, the LC components have a better filtering action against spikes ect,
> but they can add their own emc problems if one isn't careful.

One thing to remember is that most inductors start looking like
capacitors at sufficiently frequencies, while most capacitors start
looking like resistors or inductors.

-------
Bill Sloman, Nijmegen

Relevant Pages

  • Re: Simple but Fundamental Antenna Question
    ... >> circuits as consisting of lumped components (resistors, capacitors, ... A whip antenna may be visualized from ... >> circuits) as a long chain of little inductors with small capacitors ... >> available to soak up magnetic and electric fields from the next part ...
    (sci.electronics.basics)
  • Re: My capacity to react
    ... but in reality all capacitors & inductors have some ... That resistance will offset the phase shift slightly. ... It is important to note that the losses in an inductor are not limited ...
    (alt.guitar.beginner)
  • Re: Nationalized Health Care Preview?
    ... inductors and capacitors in Excel, ... destructive interference to constructive interference. ... lots of big inductors in series. ... Any time-symmetrical waveform will only contain even harmonics. ...
    (rec.arts.sf.fandom)
  • Re: Paralleling caps to meet ripple current requirements?
    ... The cap between inductors would normally see ... final cap, you have to deal with where that current goes. ... to get the most use from those capacitors and minimize ... magnetic fields caused by the ripple. ...
    (sci.electronics.basics)
  • Re: Sony KV-T25SZ8 TV problem
    ... > Capacitors are normally open circuit for DC, what do you mean by this? ... I'm wondering if my meter is stuffed. ... leg and then take the measurement. ...
    (sci.electronics.repair)