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View Full Version : Math help Rise time / Capacitance of buss tR/Cbus

metron9
09-10-2006, 09:37 PM
When it comes to datasheets, I am trying to understand every detail as best as I can but sometimes an example of real data would help my understanding. Even though I can make it work without knowing it.

I am working with the Ramtron FM24C64. There is a formula to find the maximum restor to use for a two wire buss on page 3. (link to datasheet link.. and attached schematic showing formula)

www.datasheetcatalog.com/datasheets_pdf/F/M/2/4/FM24C64.shtml (http://www.datasheetcatalog.com/datasheets_pdf/F/M/2/4/FM24C64.shtml)

The Table shows three sets of data MIN and MAX values
Are these three sets 4.5V 5V and 5.5V conditions?

tR= Input Rise Time
Cbuss = Capacitance of the buss
Questons
1. Is this correct interpretation?
2. How would one measure Cbus

Last question is Capacitance value for the formula, is it in Pf?

So Rmax=tR/Cbuss
at 5V tR=300 ns
If my buss capacitance was 100pF

300/100 = 3

So as you can see, I am lost on this minor detail.

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Think outside the BOX!

MikeK
09-11-2006, 09:26 AM
300ns / 100pF = 300E-9 / 100E-12 = 3E+3 = 3K ohms
(I'm just commenting on the math, not on whether the underlying assumptions are correct)