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UCD90320: VREFA design check for external 3V of LDO for VREFA+

Part Number: UCD90320

Hi

UCD90320 VREFA+ specification is 2.4V~3V, but your reference design used 3V output LDO (REF5030A) for UCD90320 VREFA+.

That LDO(REF5030A) could be over 3V that out of VREFA+ specification. Does it have any risk for this design?

Why don't use 2.5V~2.8V LDO for the VREFA+?

Thank you so much.

Frank

  • Hello

    REF5030A is a low drift, very high precision(0.05%) voltage reference device and it will not over the VREFA spec of the UCD90320.

    You can use 2.5V reference design if you feel more comfortable. 

    when using 3V reference, 2.5V rail does not need a external voltage divider

    Regards

    Yihe

  • Hi

    Although REF5030A is high precision LDO, but LDO output 3V*(1+0.05%) still over specification.

    What it could be problem if VREFA+ over 3V spec?

    How many tolerance for the VREFA+ spec?

    Regards

    Frank

  • Hi 

    The ADC reference value is fixed once set in the GUI. so even the vref is changed to 3V + 0.05%. Device still treat the reference as 3V. 

    You do not have to worry about the out of spec of REF5030A. but choose a reference which has high precision to get better accuracy.

    Regards

    Yihe

  • Hi

    Thank you for your explanation.

    VREFA+ spec of maximum is 3V on datasheet because of the ADC reference value highest is only 3V, so even over spec to 3.01V(1%) or more highest 3.3V(10%) that only effect the ADC accuracy, doesn't damage the chip or cause other abnormal status, is that right?

    Regards

    Frank

  • Hi

    It does not damage the device but you have a inaccurate ADC reading.

    Regards

    Yihe

  • Hi

    Could we know why the reference design that use 3V for VREF+? 

    What are the advantages of this design?

    Regards

    Frank

  • Hello

    Using external reference improves the ADC accuracy. Data sheet has the total error of both internal and external reference.

    Using 3V as external reference is to save voltage divider resistor for 2.5V rail which is quite popular in the application.

    Regards

    Yihe