[SI-LIST] Re: commom-mode current limit on hard disks

Hi Jan,

Intesting you ask.... I am writing a paper for the EOS/ESD Symposium
(next October) on the relationship between external stimuli and
potential damage to GMR heads inside. So far I have collected some very
interesting data. Unfortunately, I can't release it until the paper is
published. Once that happens in early October, I will post the paper on
my website (http://emcesd.com). I have already posted a paper there on
how to melt a GMR head with the EM radiation from a remote ESD event
which you may find interesting.

The data I have collected so far is on impulsive events which are a much
more likely threat because of high amplitudes (small ESD event from
inserting a disk, for instance). GMR head damage is likely more of a
problem than signal corruption and does not take much additional energy.
Current drives are OK, this paper will help designers for the next
generation of drives.

Doug

Jan Vercammen wrote:
> 
> Hello si-list,
> 
> I have a question concerning hard disk immunity with respect to common-mode
> (CM)
> currents on it's cables, that is, what is the maximum limit (very likely
> frequency dependent)
> of CM currents on the power port and/or data cable.
> 
> The CM currents are due to parasitic capacitive (or possible conductive)
> coupling between
> the hard disk and the chassis. The parasitic CM currents interfere with the
> disk operation
> during read/write operations, which use sensitive analog signals and are,
> as such, prone
> to intereference from these stray currents.
> 
> I have seen specifications of CM current limits of amplitude versus
> frequency.
> 
> In the past I have had a good repsonse from IBM people on this list. I was
> hoping that
> they or others could contribute some information on this topic.
> 
> Kind regards,
> 
> Jan Vercammen
> EMC/SI Engineering
> Agfa-Gevaert NV, Belgium
> 
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