Re: [SI-LIST] : Interfacing 3.3V device with 2.5V device.

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From: S. Weir (weirsp@atdial.net)
Date: Thu May 17 2001 - 20:22:57 PDT


Jinto,
If the mfg really says that it is 3.3V tolerant, then take them at their
word. I would only ask them to clarify Iin @ 3.3V.

Your best alternative is probably a QuickSwitch device powered from the
3.3V rail. This will pinch the current flow towards the 2.5V device,
limiting the swing there to about 2.7V maximum. You will have to look at
the specific data sheets for the bus width that you want. On the 3.3V
side, the entire 2.5V swing will appear, so assuming it is 2.0V Vih max,
and your system isn't aggregiously noisy, you are set. You can get those
QuickSwitch devices in low resistance, about 3-7 ohms, or medium resistance
flavors, 25-35 ohms. Use the former for minimum timing impact, the latter
if you want series termination on one side.

Regards,

Steve.
At 08:28 PM 5/17/01 +0530, you wrote:
>Hello Everybody !
>
> I have an application where I have to interface a 3.3V LVTTL I/O
> with a 2.5
>V LVCMOS I/O. The 2.5V LVCMOS is claiming to be 3.3V tolerant. I have the
>following doubt.
>
>Even if the manufacturer of the 2.5V claims that the device is 3.3 V
>tolerant, is it really advisable to subject it to 3.3V signals continuously
>? Will it have an adverse effects on the long term reliability of the device
>?
>
> Do anybody has suggestions for devices which can do this 3.3V to 2.5V
>translation for a bi-directional bus.
>
>Regards
>Jinto
>
>
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