Andy Jancura wrote:
..........
>>
>>I looked at this a little further since mentioning the transzorbs
>>yesterday. The lower voltage devices, which you would want to use
>>to help protect chips, have a substantial parasitic capacitance
>>- about 800 pF [much lower for higher V types]. Therefore they
>>are not going to be very useful for "high" datarates, except
>>possibly as part of a low-pass filter designed especially for
>>the app.
>>
>>Xc = 1/[2*pi*F*C] = 1[2*pi*100Khz*800pF] = 1900 ohms @ 100Khz
>>
>
>Dan, when you need protect High-Speed lines like satelite comunication,
>there are other tricks to do that. I just wanted to give a point, where to
>start the design. And it's allways signal bandwidth. When transzorbs are not
>useable, then other circuits may do the same job. What do you think?
>


Yes, of course, there are many different approaches to this
problem, transzorbs being only one.

Several years ago, I consulted with a company that used embedded
controllers in industrial refrigeration units. This environment
has horrendous ESD problems. We tried many ways to toughen the
units, but through a process or trial and error found that
transzorbs were the best defense, among several others, on the
units.

This did not really involve "high-speed" datacomm, and my
calc from last time shows you probably have to go to something
other than transzorbs in such a case. However, for a very low
line impedance, you could still get reasonable performance when
using TVS:

Fbw = 1/[2*pi*R*C] = 1/{2*pi*50*800pf] = 3.9 Mhz

best regards,
- Dan Michaels
Oricom Technologies
http://www.users.uswest.net/~oricom
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