Andy,=20 Thanks for the very insightful comments. On closer observation=20 the currents is due to reverse biased leakage. I did get in touch with our foundry vendor and they confirmed my observation.=20 But I am still not convinced why there should be any reverse biased leakage and if I should indeed include these in the GND clamp curves. Thanks Rohan=20 -----Original Message----- From: Andrew Ingraham [mailto:a.ingraham@xxxxxxxx] Sent: Wednesday, December 15, 2004 7:43 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Strange Gnd Clamp V-I curve when generating IBIS=20 How do you know the current is due to the GND clamp? Are you measuring = it at the clamp diode, or at the I/O pin? Normally we measure clamp currents (for IBIS models) at the I/O pad or = pin, and from there you can't really tell whether the current goes into the Ground clamp or the Power clamp. You'll see both GND and Power clamp currents, added together. It's up to you to separate it into the GND = and Power clamp curves. GND clamp currents can happen anywhere from -Vcc to +2Vcc. If your = device has positive overshoot clamps that connect to Vss (zener diodes or = active clamps, for example) and are not Vcc-relative, then I believe it would = be correct to make them part of your IBIS model's GND clamp curves, not the Power clamp curves which represent leakage and clamp currents that do = track with Vcc. Are the currents above +2.5V significant? If they are in the microamp = (or less) range, they may be "normal" for your particular device, and = hopefully this much leakage current is listed on the spec sheet. Check with the device's designers to see if this is normal. (It has nothing to do with IBIS.) Personally, I take the phrase "5v tolerant" with a gallon of salt, and = want to see further proof. Some manufacturers use that phrase despite the = fact that their devices sink large currents at, or even below, 5 volts. I suppose they believe "5v tolerant" just means the chip won't blow up if = you apply 5 volts to the pins. Regards, Andy ------------------------------------------------------------------ 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: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: =20 //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 =20 ------------------------------------------------------------------ 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: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //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