Re: [SI-LIST] : Input switching threshold & CPCI

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From: D. C. Sessions (dc.sessions@vlsi.com)
Date: Wed Jan 05 2000 - 09:13:47 PST


"Ingraham, Andrew" wrote:

> However, are you certain this model is for a part with 3.3V signaling
> levels? It's possible that this part is designed for "5V" switching levels
> but is powered by 3.3V (has 5V-compatible 3.3V outputs and 5V-tolerant
> inputs). The "VCC5REF" node is suspicious ... what would this be for in a
> 3.3V PCI signaling environment?

High-side clamping. 5-v tolerant 3.3v devices need to bias the N-well up
to 5 volts to keep the parasitic drain-well diodes of the P-channel devices
from forward-biasing. (The gate logic behind them is -- ahem! -- exotic.)

-- 
D. C. Sessions
dc.sessions@vlsi.com

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