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F2812 ADC output fluctuates

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s_cihan_tek

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Hi all,

I'm trying to use the ADC on the ezDSP F2812 development board.
I made a simple voltage divider in a breadboard using resistors and
then buffered it with a voltage follower before sending it to the
ADC pin for experimenting with the ADC. The breadboard is powered by
a 3V3 voltage regulator. (It doesn't take it power from the board)

When i looked at the output values of the ADC while debugging in CCS,
i saw that the output values of the ADC aren't 1101 and fluctuate btw
1000-1300 for an input voltage of 812mV. What could be the reason of this?

Another weird thing is, when i measured the voltage between the pins
ADCINA0(P9-PIN2) and GND(P9-PIN1) after the circuit on the breadboard is powered off, i saw 0.450V. Similarly, there were 0.730V btw
these pins when i left them floating. I don't know if this is a problem.

I'm using the internal voltage reference and a slow ADC clock
(2.5Mhz). I also made all ADC connections as in the example thermoelectric cooler design in TI appnote SPRA873 and ADC ref. guide. (AGND and VREFLO are connected etc.).

Thanks in advance
 

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