ADC problem

Posted on May 17, 2011 at 12:05

Hi,

I'm working with the UPSD3334DV.

The analog supply voltage is 3V3 and the Vref is 2V5.

The ADC operates at 12MHz.

The board has been designed with two planes one for the GND and the other one for the 3V3. The supply is free of noise.

The problem is that the result of the ADC is not constant, it is going up and down appx. 10 points.

The problem increases with lower clock !

The second problem is that the input of the analog MUX modify the voltage of the input is measuring ? ( I'm working with high impedance NTC sensor 25Kohms).

Tell me if you know those problems. I'm looking for a solution.

Thank's

:)

Posted on May 17, 2011 at 12:05

Hi,

are you using 5V signals on port 1 as well? If yes, this may be your problem.

Furthermore you could send the CPU core in suspend while running a ADC cycle. This will help you to decrease noise.

Regards,

Stefan

Posted on May 17, 2011 at 12:05

Hello

I have a Problem on ADC uPSD3333D linéarity...but not instability

I m French, please send a mail at

mailto:dmairet@best.fr

to discuss it ?

tanks

Posted on May 17, 2011 at 12:05

Hi !!

I'm not using 5V on the board.

But I have seen in the uPSD3300 erratasheet that some devices had accuracy problems with the ADC prescaler....

I asked ST if this problem concerns the devices I am working with.

I do not have any answer....

Thanks for your reply sdaxenberger !

;)