AW: [SI-LIST] : Effect of low Zo for unterminated lines

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From: [email protected]
Date: Mon Oct 25 1999 - 15:44:47 PDT


I think I have to clarify my point: I am not favoring to use lump
load model for real board design. This rule of thumb is used to
calculate the max. allowable current running through the pin.
Then if the load is a transmission line case, you can use the
figure from the above method to constrain your average current in
order to retain the chip reliability standard. Of course this
suggestion is usually good for chips specified with a capacitive
load; e.g. LVC245 as stated in the original posting.


---------------------- Forwarded by Raymond Leung/QSA/AU on 26/10/99 08:33

"Andreas Lenkisch (Trenew)" <[email protected]> on 26/10/99 22:55:44

Please respond to [email protected]

To: "'[email protected]'" <[email protected]>
cc: (bcc: Raymond Leung/QSA/AU)

Subject: AW: [SI-LIST] : Effect of low Zo for unterminated lines


it seems that we think very close to each other, but it was expressed by
different words. You favorite the current into the line capacitance (including
loads) for an estimation, I believe that the current into the line impedance,
assumed as a ohmic load may used for an estimation. But on my simulations, I
look at first for the waveforms and when I'm happy, I make a cross check for the
current absorbed from the clamps to be absolutely sure not to overstress a
component and reduce the live span.
Thank you for your discussion.


Von: [email protected][SMTP:[email protected]]
Gesendet: Montag, 25. Oktober 1999 01:13
An: [email protected]
Betreff: AW: [SI-LIST] : Effect of low Zo for unterminated lines


It is very true that a responsible chip designer should handle the
reliability issue very conservatively in order to keep your product
robust. Besides, electromigration is a life span problem. The
conservative figure of the running current is trying to assure the
mean time of failure which for a ordinalry chip should be higher
than 10 years. The other thing is if the ambient temperature is alway
kept much lower than the max. limit, say, 70C, the life time is much


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