Re: [IBIS-Users] Warnings in V-t curves

Hello Sudarshan:

I would have to see the full buffer model you are using in
case there are other surprise issues.

However, based on the waveform
information you supplied, the buffer appears to be Open_drain
or else have a very weak [Pullup] table.  The rising and falling
waveform maximum endpoints are just the V_fixture voltage of  2.5 V.

You do not give the R_fixture value, but I assume it is in the
order fo 50 ohms to get the votage swings.

The timing load test case of Rref/Vref is 1e9 and 0 V.  Even if
the voltage is changed to 2.5 V, the 1e9 resistance is still
too large to cause the buffer to reach any reasonable Vmeas
voltage.

Try using 50 ohms to 2.5 V.  The actual values are based on the
timing delay specification reference setup and referenced to
the pad voltages.  The Vmeas value would have to be between
1.25 and 2.5 V, consistent with the Rising and Falling Waveform
tables.

Bob


Sudarshan Honnudike wrote:
> 
> Hi Experts,
> 
> I am getting the following warnings while running ibischk3 on the buffer 
> models.
> 
> WARNING - Model 'bsppon3mchpt3v3_p': TYP VI curves cannot drive through 
> Vmeas=0.6V
>           given load Rref=1e+09 Ohms to Vref=0V
> WARNING - Model 'bsppon3mchpt3v3_p': MIN VI curves cannot drive through 
> Vmeas=0.6V
>           given load Rref=1e+09 Ohms to Vref=0V
> WARNING - Model 'bsppon3mchpt3v3_p': MAX VI curves cannot drive through 
> Vmeas=0.6V
>           given load Rref=1e+09 Ohms to Vref=0V
> 
> Our buffer models will be operating at 2 voltages coreside voltage and 
> pad side voltage.
> In this case, coreside voltage(VDD) is 1.2 v and pad side voltage(VDDE) 
> is 2.5v. So in V-t waveforms
> 
> 1. Rising waveform with R_fix connected to VDDE(2.5v): waveforms are 
> varying from 1.249v to 2.5v
> 2. Falling waveform with R_fix connected to VDDE(2.5v):waveforms are 
> varying from 2.5v to  1.254v
> 
> I have a confusion regarding the selection of Vmeas. Should it be half 
> of corevoltage(1.2/2) or half of pad voltage (2.5/2)?
> Please let me know how this parameter is used in the application (may be 
> in SI or somewhere else).
> 
> I even changed Vmeas to 1.25 V. Still I am getting warnings like
> 
> WARNING - Model 'bsppon3mchpt3v3_p': TYP VI curves cannot drive through 
> Vmeas=1.25V
>           given load Rref=1e+009 Ohms to Vref=0V
> WARNING - Model 'bsppon3mchpt3v3_p': MIN VI curves cannot drive through 
> Vmeas=1.25V
>           given load Rref=1e+009 Ohms to Vref=0V
> WARNING - Model 'bsppon3mchpt3v3_p': MAX VI curves cannot drive through 
> Vmeas=1.25V
>           given load Rref=1e+009 Ohms to Vref=0V
> 
> Please let me know your answers.
> 
> Best Regards,
> 
> Sudarshan HN
> NXP Semiconductors/CTO /PLT
> # 1 Murphy Road, Ulsoor, Bangalore - 560 008 , India.    
> Ph:+91-80-40247073  
> Fax: +91-80-4024 7855
> seri:sudarsha@inpsblr
> E-mail: sudarshan.honnudike@nxp.com


-- 
Bob Ross
Teraspeed Consulting Group LLC     Teraspeed Labs
121 North River Drive              13610 SW Harness Lane
Narragansett, RI 02882             Beaverton, OR 97008
401-284-1827                       503-430-1065
http://www.teraspeed.com           503-246-8048 Direct
bob@teraspeed.com

Teraspeed is a registered service mark of Teraspeed Consulting Group LLC

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