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

Hello, Sudarshan,

1) Please use ibischk4.  This is capable of checking [IBIS ver] 3.2 models.
Bug fixes and enhancements are not patched back into older versions of
ibischk.

2) Rref, Cref, Vref and Vmeas are used for hardware testing, and should be
on the I/O data sheet or on the I/O interface specification.  Vmeas is
normally between Vinl and Vinh.

3) Rref default value is 50 ohms.  1E+9 is not a reasonable value.

4) Vcc_core is not used in the IBIS model.  It is used only in simulation to
drive the "core" pins (Enable, Data) on the I/O buffer.

5) There are two good sources of modeling help.  These are the
 IBIS Cookbook http://www.eigroup.org/ibis/tools.htm 
and the IBIS Quality Checklist http://www.vhdl.org/pub/ibis/quality_wip/


Best regards,
Lynne


"IBIS training when you need it, where you need it."

Dr. Lynne Green
Green Streak Programs
http://www.greenstreakprograms.com
425-788-0412
lgreen22@mindspring.com- Lynne

 


________________________________

	From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On
Behalf Of Sudarshan Honnudike
	Sent: Tuesday, November 07, 2006 9:25 PM
	To: ibis-users@eda.org; ibis-info@eda.org
	Subject: [IBIS-Users] Warnings in V-t curves
	
	

	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



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