STR912 ADC problem

[yuri2]

Posted on June 09, 2007 at 11:09

STR912 ADC problem

[yuri2]

Posted on May 17, 2011 at 09:36

We use STR912FW44X rev D chip (19 week of 2006). AVDD connected to 3.3V analog supply and AVREF connected to 1.22V analog reference. ADC did not work properly. With 0.8V on analog input, I got overflow (ADC_DRx register equal to 83FF). The same behavior both on IAR development board and on our board.

Experiment shows, that ADC start to work, then AVREF above 1.5 volts. However, operating conditions for AVREF are in the range from 1 to 3.6 volts (table 4 of the 12274.PDF).

Can anybody explain where is my mistake.

[ivo2]

Posted on May 17, 2011 at 09:36

Hi Technor,

Could you please post the ADC SCU and GPIO settings you are using? I suppose the problem should be there.

[amira1]

Posted on May 17, 2011 at 09:36

Hi technor,

FYI

the Input Voltage is in the range from 0 to 3.3V (see table 24 datasheet). Hence, in this range the ADC work properly.

You can try the ADC STR9 library example to confirm this range.

Best regrads,

mirou

[ This message was edited by: mirou on 26-02-2007 08:53 ]

[mark9]

Posted on May 17, 2011 at 09:36

I'll act as English translator:

Mirou said that his ADC does NOT properly convert Vin=0.8V if AVREF=1.22V but it does convert if AVREF>=1.5V. A 0.8V input with 1.22 reference should be 0x3FF*(0.8/1.22) = 0x29F but he gets 0x83FF (overflow).

The spec states that AVREF is allowed to go down to 1.0V.

I am curious to know what the solution to this problem is.

[mark9]

Posted on May 17, 2011 at 09:36

I just noticed this is now official part of the Errata (rev 5). AVref must be >= 2.6 V