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UCD3138064: Using EADC as continuous SAR

Jack Wang
Intellectual 310 points
Part Number: UCD3138064
Other Parts Discussed in Thread: UCD3138

Greetings Experts,

 - In SLUSAP2 A 2012, UCD3138 Highly Integrated Digital Controller for Isolated Power Data Manual, Page 16. The table shows "EAP-EAN Error voltage digital resolution" has a range of 0.95mV to 1.2mV when AFE_GAIN = 3. Does it mean when 100mV is present at the Front End, I may get ABS_VALUE from 105 to 83?

100mV / 0.95 mV = 105.26

100mV / 1.2 mV = 83.33

Thanks for your help.

  • 0
    TI__Mastermind 18370 points

    Hi Jack,

    The short answer is no.


    But here is a more complex answer:

    There are two different types of resolution that are involved here.

    The "absolute value resolution", which regardless of the AFE gain setting is 1.5625 mV/bit.
    Meaning that for 100 mV your absolute ADC count will be 100/1.5625 = 64 counts.

    Then you have an "error resolution" that depends on AFE setting and it is typically 1mV/bit for AFE=3.
    But since the AFE gain and everything else has a tolerance, it can be actually 0.8mV or 1.2mV/bit (+/-20% of tolerance).

    You should not think about this resolution as a way to calculate the counts for your input voltage.
    You should rather think of this error resolution as the minimal change that can still be sensed/recognized by the EADC at AFE=3.

    AFE setting does not change the overall ratio between the analog input and the digital output. But it just changes the EADC's front end sensitivity.

    Hope this makes sense.

    Regards,

  • 0 in reply to Yitzhak Bolurian
    Intellectual 310 points

    Hi Yitzhak,

     - Got it. Thanks a lot.