Re: [SI-LIST] : Non-standard bus termination (2nd posting)

jrbarnes@lexmark.com
Wed, 22 Sep 1999 10:32:35 -0400

BI Technologies has an RC6 series with up to 8 RC terminators in a 6.4mm x 3.2mm
(0.252" x 0.126") 10-pad chip. The resistors can be 20 ohms to 1 megohm, while
the capacitors are a maximum of 50pF in an 8-terminator part.

AVX has a |Z| Chip line with up to 4 distributed resistance/capacitance
terminators in an 0612 (0.06" x 0.012") package.

Page 234 of Mark I. Montrose's book EMC and the Printed Circuit Board
suggests that the resistance of an RC-termination match Zo of the trace, while R
* C be at least twice the loaded propagation delay (round trip travel time) of
the signal.

John Barnes
Advisory Engineer
Lexmark
International

massimo.polignano%esaote.com@interlock.lexmark.com on 09/22/99 04:45:29 AM

Please respond to si-list%silab.eng.sun.com@interlock.lexmark.com

To: si-list%silab.eng.sun.com@interlock.lexmark.com
cc: (bcc: John Barnes/Lex/Lexmark)
Subject: [SI-LIST] : Non-standard bus termination (2nd posting)

Has anybody out of there any suggestion about the following problem? (I think it
is quite a common one).

I?ve got a board with a non-standard bus of 34 traces. The bus drives a group of
memories.
The lenght of the bus is necessarily higher than the critical lenght (lcr =
tr/2tpd): a termination could be useful. The problem: there are so many traces
that one has to use too many components (34 resistors and 34 capacitors for AC
parallel termination).

What shall I do?
Are there any special components (array) to terminate this type of bus?
Shall I terminate the bus or not? (In past experience not always a termination
was mandatory)

Thanks for any help.

m.p.

---------------------------------------------------------
ESAOTE S.p.A. Massimo Polignano
Research & Product Development Design Quality Control
Via di Caciolle,15 tel:+39.055.4229402
I- 50127 Florence fax:+39.055.4223305
e-mail: massimo.polignano@esaote.com

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