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'Current drawn by an ANx input ? 16F690'
2010\07\29@101513 by Jan-Erik Soderholm

face picon face
PICkit2 with low-pin-count board (16F690).

That board has a 10k pot with a 1 k resistor
connected between the wiper and the AN0 input.

Now, when running the ADC-demo program (number 4 of the
lessons, called ADC.ASM), I can see a larger then I
expected voltage drop across the 1 k resistor. Up to
0.85 V when the pot is at the 5V end. That is, there
must go aprox 0.85 mA into the RA0/AN0 pin.

Is that expected ? I've read the datasheet back and forth
but can not find any note sayig that the AN0 input should
draw that amount of current. A few uA's leakage maybe...

It doesn matter if I put a 1 sec delay between the ADC
conversions, the voltage drop across the 1k resistor
stays the same.

What is going on ?

2010\07\29@102628 by Michael Rigby-Jones


> -----Original Message-----
> From: [] On
{Quote hidden}

Yes that is unexpected in normal operation, the average current into an
analog pin is very small, certainly in the uA's.

Is the top of your potentiometer definitely powered from the PIC's Vdd
rail?  If you exceed Vdd then you will be pumping current into the PICs
protection diodes.



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