>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>On Behalf Of PicDude
>Sent: 20 April 2007 19:06
>To: Microcontroller discussion list - Public.
>Subject: [PIC] Current limiting resistor effects
>
>
>
>Thoughts?
>


I think you may be over thinking this :D

1) The datasheet recommends a maximum source impedance of 10k, you are significantly below this, even with the 1k series resistor (worst case 1.27k). Providing your aquisition times are set correctly, you should not experience any degradation in accuracy.

2) The absolute maximum current into the protection diodes is shown in the asbolute maximum ratings table as "Input clamp current" and "Output clamp current" which are both 20mA.

3) I would be concerned about the effects of 14v on the input pushing Vdd up via the 270R resistor.  That's a current of 14-5/270 = 33mA being pumped into your Vdd rail.  If the circuit consumes less than this current the rail voltage will rise.  A zener clamp on the rails would be a good idea, if not already present.

Regards

Mike

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