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UCD3138: ADC error

user5952325
Intellectual 455 points
Part Number: UCD3138

I applied a voltage to the ADC of UCD3138 in the range of 1.2V-1.5V. 

The AD value showed a voltage about 20 mV lower(-1.5%) than the applied voltage. 

I want to measure the AD value with high accuracy. Does an error of about 20 mV often occur? 

I checked the data sheet'UCD3138 Highly Integrated Digital Controller for Isolated Power'. 

Can the internal ADC reference voltage, ADC Zero Scale Error, and ADC Full Scale Error be the causes of the 20 mV error?

Is this error a variation or a normal deviation?

Is the error of the Internal ADC reference voltage included in the error of ADC Zero Scale Error and ADC Full Scale Error?

  • 0
    TI__Mastermind 18370 points

    Hi,

    Could you please tell us a bit more about your power stage topology and power level?

    Have you connected your voltage source directly to the ADC input or through a resistor?

    Do you have any anti aliasing capacitor at the ADC input?

    What are the other ADC inputs connected to?

    What is the operating temperature range of your application?

    Please advise and I will try to assist accordingly.

    Regards,

  • 0 in reply to Yitzhak Bolurian
    Intellectual 455 points

    Have you connected your voltage source directly to the ADC input or through a resistor?
    The voltage is input through a 100Ω resistor.

    Do you have any anti aliasing capacitor at the ADC input?
    There is a 1000pF capacitor at the ADC input.

    What are the other ADC inputs connected to?
    Some ADCs are connected to ground. The other part is not connected.


    What is the operating temperature range of your application?
    Temperature range is 10℃-20℃.

  • 0 in reply to user5952325
    TI__Mastermind 18370 points

    Thank you for the provided feedback.

    Is your application's entire temperature range between -20C to +10C and never goes beyond this range?

    What is your power stage topology and power level? Please advise.

    You may as well consider the use of UCD3138A (new revision) which offers improved ADC accuracies.

    Regards,

  • 0 in reply to Yitzhak Bolurian
    Intellectual 455 points

    The temperature range of the application is -20 ° C to 55 ° C.

    However, the AD value, which shows a voltage (-1.5%) about 20 mV lower than the applied voltage, was recorded only on the printed circuit board at a temperature of 10 ° C.

    The power stage topology and power level are 2.7kW DCDC converters.

    However, the test conditions were the same as above, only the printed circuit board, and the temperature was 10 ° C.

  • 0 in reply to user5952325
    TI__Mastermind 18370 points

    Hi,

    If you measure your voltage twice by having this channel measurement twice in the sequence, you might be able to minimize the Cross talk effect and get a closer measurement.

    20 mV is actually 20 mV/2500mV = 0.8% of the full range for the ADC.

    What is your power stage topology?

    Is it PFC? Full bridge? LLC? Please advice.

    Regards,

  • 0 in reply to Yitzhak Bolurian
    TI__Mastermind 18370 points

    Hi Kyohei Morioka,

    Any comments?

    Another option for more accurate measurement can be use of EADC in SAR mode.

    EADC offers a dedicated (non multiplexed) measurement channel, so no cross talk involved.

    Please just get back to me with the answer to my questions, and I will try to provide a solution accordingly.

    Regards,

  • 0 in reply to Yitzhak Bolurian
    TI__Mastermind 18370 points

    Hi Kyohei Morioka,

    Since we have not heard from you for a while, I am closing this post.

    Hope your concern was addressed.

    If any questions left, please open a new post and raise your questions again.

    Regards,