ADC is temperature dependent?

[ezanen9]

Posted on November 16, 2006 at 08:43

ADC is temperature dependent?

[ezanen9]

Posted on November 16, 2006 at 05:02

Hi all,

I am working with the STR710 MCU. I am using it in an application where the MCU itself and the PCB where it is place on can become 60 degrees celcius. If I start at room temperature(25 deg) and I readin an analog input it outputs for example 2354. Now I keep the analog input voltage stable within the 1mV. If the temperature rises to about 60 begrees the analog value I read in decreases to about 2352/2351. Does this mean that the ADC of the MCU has an temperature dependence? (For reasons I have to read in at maximum resolution, temperature dependence is not allowed) If so what can I do about it? Thanks, Jimmey

[hichem2]

Posted on November 16, 2006 at 05:59

Hi Jimmey,

Some characterization tests are done on the STR71x ADC12 converter in a temperature range of -45°& 130° and find bellow the results: - The Vcm is measured between 1.232v and 1.29v for all temperatures, and vcm decreases (20mv less between 45° and 130°) when temperature increases. - The offset code is between 94b and 9ac for all temperatures, offset decreases when temperature increases. - The 2.5v gain code is between 61d and 69b for all temperatures, gain increases when temperature increases. In the other hand, for more details concrning the PCB implementation please refer to section: General PCB Design Guidelines (STR71x Datasheet Rev.10, page 64/75). I hope that this can help you, Regards, hich

[ezanen9]

Posted on November 16, 2006 at 08:43

Thanks for the answer Hich,

The input readings of this analog input are very stable. And I followed the PCB guide lines. The ADC outputs the same value's on fixed analog input signals. So I think that my error does not come from(noise)errors in the hardware. I runned a few more tests and I am reasonable sure that the temperature change from 25 degrees till about 60 degrees is causing an offset of 2 of 3 ADC steps(from 2354 down to 2351). Why does the output value decrease as the temperture increases? What is your opinion is the(best)way to solve this problem? Can I do it in software only? Or do I have to add hardware?(all my PCB's are already finished, so I rather do not change any hardware) Or do you perpaps you have additional data for me? Like temperature v.s outputvalue of ADC. Regards, Jimmey