This works really well. If your design is unidirectional and is not=20
open-collector, you can do each line with one mosfet and one resistor. =20
Change the pull-up voltage on the output side to 3.3V or 5V as you need.
http://www.nxp.com/documents/application_note/AN10441.pdf

Cheers,
-Neil.


On 8/26/2012 11:07 AM, peter green wrote:
> I want to take a group of 3.3V logic signals, buffer them and output
> them as either 3.3V or 5V logic signals at the board users selection.
>
> I first thought of using a normal logic chip but I can't seem to find a
> family that has 3.3V compatible inputs when running off 5V and is
> specced to run off 3.3V and I'd rather users didn't have to swap chips
> to change the output voltage.
>
> I found a chip from TI that can do such conversions, the SN74LVCC3245
> but it seems to have painful power up requirements (according to Ti Vcca
> must come up BEFORE vccb). I guess I could put in a RC circuit or
> something to slow down the coming up of Vccb but it seems a messy solouti=
on.
>
> Any thoughts/advice on this.

--=20
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