ADS7841-Q1: Additional information for specifications

Hello,

-Total Uncalibrated Error (TUE)  is a static or DC error estimate, which represents the deviation between the actual and the ideal transfer functions of an ADC. This specification assumes that no system level calibration is performed. Conceptually, the TUE is the combined effect of the following static parameters:  offset, Gain, linearity, and may incorporate any other offset, accuracy or Gain errors that may be present in the system (for example driver amplifier offset, gain, and external ADC reference errors.   This specification quantifies the DC or static accuracy of the system or ADC. 

As you have mention, TUE is an estimate of error using the Root Sum of Square (RSS) of un-correlated parameters.   If you calculate ADC TUE based on the maximum offset, max INL, and Max Gain errors given in the datasheet, it is very unlikely that you will find a device that will exceed  this TUE estimate.
However, it is important to mention, TUE is an estimate of error and TI only offers a guarantee on the min/max parameters as specified on the electrical table of the datasheet.

- We do not offer a guaranteed minimum spec for current consumption.  Looking at a typical distribution spread  for current  with VCC=5V,  Fsample=200kHz, at 25C, the quiescent current minimum is expected to be approximately ~500uA.

- Best practice is to connect the unused inputs to GND using a pull-down resistor.

- The ADS7841-Q1 is an automotive grade device and it has AEC-Q100 certification.

Thanks and Regards,

Luis

Hi Luis

Thank you for your reply.

Regarding to the TUE calculation, do you have some reference document that explains TUE can be estimated using RSS?

Or is it commonly used method?

- Best practice is to connect the unused inputs to GND using a pull-down resistor.
Is 4.7K - 10K resistor practical?

- The ADS7841-Q1 is an automotive grade device and it has AEC-Q100 certification.
Can we regard all Q1 devices have AEC-Q100 certification?

Is it possible to confirm it on some kind of materials?

(Because I can see the description of AECQ100 on the datasheet in some of Q1 devices (like LP8731-Q1), but the others not so.)

BestRegards

Hi Luis

Thank you for your reply.

Sorry. Could you show us a paper name (it is OK one of references) that mentions TUE defined as the RSS of offset, gain and INL?
(TUE = sqrt (sq(Offset Error) + sq(Gain Error) + sq(INL)))

We have to present reasoning.
I understand it is unusual request, but its customer's request...

Our customer is about to compare TUE with competitor.
The competitive device guaranteed maximum TUE in the datasheet, so we want to persuade them using calculation of TUE (max).

And you say INL already incorporates DNL errors by definition.
However, I think it is better to use DNL value to get more accurate TUE.
Is it correct?

If so, could you tell us maximum DNL if you have?


BestRegards

Hello,

Yes, I have found a number of publications available from different authors, some of them define TUE as the RSS of offset, gain, INL and DNL; while others define TUE as the RSS of offset, gain and INL. 

Below is the link to one publication that does not include DNL.   There are other publications from other manufacturers as well that define TUE as the RSS of offset, Gain and INL without DNL.

https://e2e.ti.com/blogs_/b/precisionhub/archive/2014/10/14/adc-accuracy-part-2-total-unadjusted-error-explained

Strictly referring to the non-linearity definition, INL(integral non-linearity) is the measure of the deviation of the code transition or code step levels from the ideal straight line, and it is defined as the maximum difference between the ideal and actual code transition levels after correcting for gain and offset.   INL can be found by computing the cumulative sum of DNL by the equation below; therefore, an ADC's INL error already incorporates DNL.   In other words, INL is the integral of the DNL errors:  

As previously mentioned, TUE is an estimate of uncalibrated total error and in the case of the ADS7841-Q1, we only guarantee the min/max specifications provided in the datasheet. 

Best Regards,

Luis

Hi Luis

Thank you for your reply.

I understood the TUE.

Sorry, regarding to Iq, please tell me the following.

You said Iq(min) with VCC=5V, Fsample=200kHz, at 25C, is expected to be approximately ~500uA.

Can you offer Iq(min) which is applicable in all temperature range?

BestRegards

Hi

Sorry to trouble you.

Do you have information?

BestRegards