ADC conversion is not stable

[Fabio Malatesta]

Posted on October 10, 2017 at 16:26

Hello!

I'm using XPC56xL minimodule on the XPC56XX motherboard.I slightly modified the SPC56ELxx OS-Less ADC Test Application to print the ADC conversion values on the UARTThe issue I noticed is that the value of the conversion is not stable: for example if I print 15 measures (all of them done without changing the trimmer position) I get the following result (in hexadecimal):

ADC Value:

278279274278277274272272275278276274276276278276

So it seems that the 4 least significant bits are given only by the noise. Since i read on the reference manual that the ADC has 12 bits resolution, i would like to know if there is a strategy to keep those bits stable.

Thank you in advance!kind regards,Fabio

[Erwan YVIN]

Posted on October 11, 2017 at 08:55

Hello Fabio ,

For a normal conversion , you have to increase PSAMP it is more stable.

Could you increase it ?

Sorry, The RM is not accurate for this point.

       Best regards

                       Erwan

[Fabio Malatesta]

Posted on October 11, 2017 at 16:18

Hello Erwan,

Thank you for your help but the situation hasn't changed: i tried several values for PSAMP (also the maximum) but those 4 LSB are still unstable.

The value should be stable, because it simply depends on the value of the trimmer resistance.

Do you have any further suggestion?

Thank you in advance for your support!

Kind regards,

Fabio

[Erwan YVIN]

Posted on October 11, 2017 at 17:15

Hello Fabio ,

I am checking with ADC experts.

         Best regards

                    Erwan

[Erwan YVIN · Accepted solution]

Posted on October 13, 2017 at 10:28

Hello Fabio ,

I have checked with ADC Experts on 12 bits conversion

the results below are good.

ADC Value: (4095 max)

278

279

274

278

277

274

272

272

275

278

276

274

276

276

278

276

    Best Regards

       Erwan

[Fabio Malatesta]

Posted on October 13, 2017 at 11:15

OK thank you Erwan!

Best regards,

Fabio