TM4C1237H6PZ: Reference error of internal ADC

Hi Charles,

Ok thanks please let me know if that was a typo or not so I can reassure customer about that.

BR,

Antonio

Hi Charles,

My customer is talking about errors when internal - not external - reference is used.
With the external reference everything is fine and the errors are the typical ones, some LSB.

Below in the same table are the characteristics when the internal reference is used.
And that's where I was amazed.

30LSB error makes a 12-bit ADC become equivalent to a 7-bit one….

Can you please check?

Thanks,

Antonio

Hi Antonio,

  Checking the offset and gain error for TM4C129 with internal reference, I find the same values with 30+/-LSB for both TM4C123 and TM4C129. I will need to check internally with someone who may knowledge on the offset/gain error for TM4C ADC. 

Hi Charles, Ok thanks please let me know once you have a solid feedback so i can share with customer.

BR,

Antonio

Hi Antonio,

  I have some feedback from our ADC designer. Please find below. 

"+/-30LSB/4096 is about +/-0.7% for internal reference accuracy which may not be so bad. 

Reference error is usually spoken of in terms of %. In this case, the gain error is caused by inaccuracies in the reference voltage is ± 0.7 %. Numbers are smaller with an external reference because a perfect external reference is assumed. If customers use this ADC with a ±0.7% accurate external reference, the gain error at full-scale would be the same ± 30LSB as if they used the internal reference instead. Customers can improve overall accuracy by paying more for an external reference with higher accuracy, say 0.1%. The gain error of the ADC by itself, with a perfect external reference is < ±3LSB/4096 = ±0.07%, so a customer paying more for a ±0.01% accurate external reference would be wasting their money."