ADC Problem Using upsd33xx

simonloo · ‎2006-04-25

Posted on April 26, 2006 at 04:12

simonloo · ‎2011-05-17

Posted on May 17, 2011 at 12:10

Dear All,

Did anyone of you solve the ADC Noice Problem? I have read all the article at this forum, but i didn't get any information to solve my problem.:-[ :-[ :-[ :-[

I am using a two resistor serial togather, one end of the serial resistor connect to 3V3, the other end connect to the GND, center of the serial resistor connect to the ADC input, i get the ADC reading not stable at all.

Did you'll having this problem before? how you solve it, Please Help! ;)

joseph2399 · ‎2011-05-17

Posted on May 17, 2011 at 12:10

For board level related suggestions, see AN2010 found at:

http://mcu.st.com/mcu/modules.php?name=mcu&file=familiesdocs&FAM=80

Better results have been obtained wiht AVref = AVcc.

Use the slowest ADC clock and put the MCU in idle mode during the A/D conversion. Use the A/D interrrupt to bring the MCU out of idle mode when the conversion is complete.

Also keep in mind that Port 1 is not 5V tolerant. Signals on Port 1 pins exceeding the 3.3V supply can affect the voltage on other port 1 pins.

[ This message was edited by: uPSD on 06-02-2006 22:04 ]

simonloo · ‎2011-05-17

Posted on May 17, 2011 at 12:10

Thankx for your suggestion, i will try it out tomorrow.... ;)

urik · ‎2011-05-17

Posted on May 17, 2011 at 12:10

Hi,

I have also faced this problem and no one at ST could help me.

I have two suggestions, based on some tests I have done:

1. Use the FASTEST ADC clock possible. This will produce less noise than slow clock as long as the drive of ADC input is not weak (resistors less than ~100K) (they probably did not put a buffer before the MUX).

2. Using the Idle mode is a must, the noise difference is quite large.

3. As strange as it may seem, do not use sector 0 of main flash (FS0) to store data/code. If this is not possible, start placing data/code from the sector bottom address, use as less space as possible. Yes, the presence of data different from 0xFF in FS0 contributes to the ADC noise (more data = more noise)!

Good luck! :)