FreeLists / si-list / [SI-LIST] Re: Termination Topology for Bidirectional Bus

[Erin.McPhalen@xxxxxxxxxxxxxxxxxxxxxxxxx]

Hi Saril
Not all logic families are designed for Parallel or Thevenin termination,  
they require substantial current drive.  For 50 Ohms termination and 3.3V 
logic, Parallel  termination would require a driver capable of sourcing 
and sinking 66 mA of current and Thevenin termination would require 33 mA.

In general, I have used series termination at each driver.   In the case 
where it is not practical to terminate every driver, Hyperlynx is very 
good tool for helping you decide on the critical drivers.   Placing the 
termination in the middle of the bus is not the intended purpose of series 
termination.   Series termination is intended to match the drivers 
impedance to that of the transmission line for the most part, it also 
serves to limit the current that can enter the trace as well.

Erin




Saril <saril_k@xxxxxxxxx> 
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[SI-LIST] Termination Topology for Bidirectional Bus






Hi,
What would be the best termination topology for a Bidirectional Data bus?

Is it a good thought to place the series termination resistor in the 
middle of the trace?

Also when there are mulitple devices on the bus how can we boil down the 
SI issues.

Its clear that HyperLinx can help on this but, it would be great to know a 
generic rule.


Thanks in advance..

Best regads
Saril Kaiprath
Design Engineer
Fkextronics Design, Bangalore


 
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