[SI-LIST] Re: Load calculation and Buffer.

8mA is the nominal output.  Look at the IBIS model for the expected V/I 
curve.  You will likely find the drive strength is much higher at the 
start of the rise / fall.  However, 8mA is still very weak for 3.3V 
swing at 200MHz+.  A 3.3V CMOS buffer such as you have selected is a 
poor choice for signaling much above 100MHz.  If you must signal with 
3.3V then at least increase the drive strength of your buffer. 

If you are just trying to characterize your ICs and/or interconnect and 
have to use that weak 3.3V driver, lower the signaling rate.

Steve.
Nirmale G wrote:
> Hi ,
>  
>
> I have 20 i/o lines from a test board to be interfaced to  FPGA for
> analysis. The test board chip pad can max drive a current of 8mA , max
> frequency is 216MHz , and logic level is 3.3V.
>
>  
>
> Calculation for load, C  = I * dt/ dv
>
>  
>
> C = 8e-3 * rise time / 3.3 
>
>  
>
> Taking Rise time  as (0.46ns)10% of period (4.6 ns) gives the  C = 1.12pF ,
> which is very less . 
>
> But, For any buffer/ line driver  the typical input capacitance is 5 to 7pf
> . 
>
>  
>
> Any thoughts on the interface and my calculations for load.
>
>  
>
>  
>
> Regards
>
> Nirmale G
>
>  
>
>
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> http://www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
> List technical documents are available at:
>                 http://www.si-list.net
>
> List archives are viewable at:     
>               http://www.freelists.org/archives/si-list
> or at our remote archives:
>               http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
>               http://www.qsl.net/wb6tpu
>   
>
>
>   


-- 
Steve Weir
Teraspeed Consulting Group LLC 
121 North River Drive 
Narragansett, RI 02882 

California office
(866) 675-4630 Business
(707) 780-1951 Fax

Main office
(401) 284-1827 Business 
(401) 284-1840 Fax 

Oregon office
(503) 430-1065 Business
(503) 430-1285 Fax

http://www.teraspeed.com
This e-mail contains proprietary and confidential intellectual property of 
Teraspeed Consulting Group LLC
------------------------------------------------------------------------------------------------------
Teraspeed(R) is the registered service mark of Teraspeed Consulting Group LLC

------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field


List technical documents are available at:
                http://www.si-list.net

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts: