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MSPM0L1304: Estimating ADC parameters for internal reference

Tanmay Sutaria
Prodigy 165 points

Part Number: MSPM0L1304
Other Parts Discussed in Thread: MSPM0C1104

Hi,

We are evauating the MSPM0C1104 and M0L1304 microcontrollers which have 12bit ADCs to replace existing FR series parts with 10bit ADCs in our measurement systems. We would like to use the internal 2.5 reference for the ADC. The operating range would be 0 - 60 degC.

The ENOB for both parts when ADC uses internal reference are specified in the datasheet as 9.8 and 10.2. The VREF TC is 200ppm/deg with an additional drift of 300ppm. 

Taking a case where the ADC is calibrated at 20deg and then signal measured at 60deg, the VREF drift would be 8000ppm, not including the additional drift. For a 12bit ADC with a FS signal of 2.5V, 1LSB = ~600uV. Does this mean that the ENOB would drop to ~5.5 bit as the 8k ppm drift will add that much error into the reading? Correct me if my understanding is incorrect. If correct, then will correction for TC be mandatory for a resolution of full 4k points of the ADC?

Secondly, the lower spec part C1104 has TC listed as 75ppm/degC which is substantially lower than that for the 1304. Would the C1104 ADC give better results than 1304 if drift compensation is not implemented or am I missing something?

Please advise at the earliest convenience.

Best regards,
Tanmay.

  • 0
    TI__Mastermind 23842 points

    Hi Tanmay,

    Could you please provide the following information?

    1. What does “full 4 k points” mean, i.e., what is an acceptable absolute accuracy or measurement uncertainty?

    2. What does your 20°C calibration cover?

    3. Does your system have access to temperature at runtime?

    4. Could you please provide the frequency, signal bandwidth, and the type of signal you intend to measure with the ADCs?

    Best Regards,

    Diego Abad

  • 0 in reply to Diego Abad Sajamin
    Prodigy 165 points

    Hi Diego,

    Thanks for the response. Sharing the required details below.

    1. By full 4K points I mean the 12 bit resolution of 4096 counts. My query is that with VREF drift, without TC correction, will the ENOB will drop? If yes this would lead to lower available/usable counts and absolute accuracy?

    3. Temperature measurement from the internal sensor, ADC channel, TLV data.

    2&4. We wish to measure true RMS of AC sinewaves from 30 - 500Hz. The wave could be full or chopped sinewave. Since the ADC is unipolar, the AC signal 'common' is tied to a 1.25V buffered 'BIAS' so that full cycle is within ADC range. Calibration at 20deg C is a two step process which first saves the BIAS voltage value and then the max signal and scales if to full scale. For the signal its a single point calibration.

    As VREF drifts the absolute accuracy of both these saved values will drift. This is what we wish to understand and estimate.

    Best regards,
    Tanmay.

  • 0 in reply to Tanmay Sutaria
    Prodigy 165 points

    Hey Diego Abad,

    Just a reminder to look into this and revert.

  • 0 in reply to Tanmay Sutaria
    TI__Mastermind 23842 points

    Hi Tanmay,
    Thank you for your patience (I was at a customer support travel last week). I'm currently investigating this inquiry, and I will get you back ASAP.

    Best Regards,

    Diego Abad

  • 0 in reply to Tanmay Sutaria
    TI__Mastermind 23842 points

    Hi Tanmay, 
    Please find the responses bellow:

    1.If the signal is maintained within the VREF range (including temperature drift), ENOB degradation will be negligible. However, if the signal exceeds this range, the ADC will saturate, resulting in significant ENOB degradation. To prevent saturation, the maximum signal amplitude must be kept below VREF − 1.5%.

    2.The L1306 have the same PPM value as the C1104. This wrong value in the datasheet will be fixed in the next release of the datasheet. 

    Best Regards,

    Diego Abad

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