Microchip 16F A/D converter VRef

[Unix]

Hi Everyone,

I have only joined a few weeks ago and this is my first post to this forum.

I am using the analogue to digital converter on the 16F690 and am going to need to use an external voltage reference for the conversion.
My question is this: can the voltage I apply to the VREF pin be greater than vdd?

I have used the A/D before using both the internal Vddref and also an external Vref which was below vdd. But can the external VRef be above Vdd? Will the chip handle the extra current without damage and will it be able to do the calculations with the Ref being between 6V - 12V?

Any help is appreciated.

Rich

[SeanB]

Simple answer is no. Either divide the reference to below the supply and similarly divide the input to below the supply rails or use a different reference that is below the supply rail. All the inputs have protection diodes that will clamp to a little above the supply voltage, and if you have enough input current the chip will turn into a pretty poor SCR and let the smoke out.

[Unix]

Hi SeanB
Thanks for the reply.

Your answer was going to be my fall back - to use a voltage divider to split up the high reference voltage.
I should have guessed that it would have been too convenient the other way..

Thanks.