16F series need somewhere between 2.5V to 2.8V.
I doubt 18F philosophy on AD is different.
The best choice could be a 3V linear regulator which gives you both
the supply and the reference. Like LT1763-3 ?

Vasile

On 10/3/06, genome <jtroxas@gmail.com> wrote:
> hello,
> Anybody can recommend 3 volt Vref Diode.. I cant use a 2.5volt such as
> LM336BZ-2.5 as the datasheet for pic18f242 says:
> (VREFH - VREFL) must be minimum of 3V when Vdd >= 3V..
> is this correct as I've heard on other PICS its 2.5volts.. maybe I could use
> a zener but unfortunately I could not find any zeners here that has 1%
> tolerance..
>
> thanks..
>
>
>
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