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How much GAIN ERROR performance can be improved of ADS8568 if we used an external reference - REF5025?

Iven Xu
Intellectual 2090 points
Other Parts Discussed in Thread: ADS8568, REF5025

Dears data converter experts,

Here I met a question about the GAIN ERROR of ADS8568,

As we can see the maxim GAIN ERROR is +-5% in ADS8568 datasheet, which test condition is based on the inernal reference of ADS8568.

Question:

If we changed the test conditiono from internal reference of ADS8568 to an external reference - REF5025, then how much gain error will be improved?

Do you have the test result/data of Gain error witht the external reference? thanks.

Best Regards

Iven Xu

  • 0
    TI__Intellectual 2090 points
    Any expert can help supoprt this question?

    Best Regards
    Iven Xu
  • 0 in reply to Iven Xu
    TI__Expert 3775 points
    Hi Iven,

    I am afraid we do not have the gain error information with external reference readily available.

    In this device, the gain error is specified referenced to REFIO. As per the block diagram, buffer is present after the REFIO node in the chip. The offset error of the buffer will contribute to gain error specification of the ADC.

    At the +-10V input range, gain error is specified at 0.5%. This translates to a total error of +-50-mV. This gain error includes error on account of ADC and internal reference buffer.

    If you readily have access to a ADS8568 EVM, You can measure the differences [REFIO-REFAP], [REFIO-REFBP], [REFIO-REFCP] and [REFIO-REFDP] to measure the offset error of the internal buffer. If this offset is the dominant factor, in 50-mV gain error, you will get improvement in gain error spec by using an external reference source.

    Using an external reference option, you will save on the gain error caused on account of internal buffer. Hence you will need to drive REFAP, REFBP, REFCP and REFDP directly (driving REFIO externally does not eliminate the internal buffer).

    Regards,
    Rahul
  • 0 in reply to RahulVK
    TI__Intellectual 2090 points
    Hi Rahul,

    Thanks for your information.
    Based on your analysis, the key factor for the gain error of ADS8568 is the internal buffer.

    I cannot test the offset error between [REFIO-REFAP], so could you please help test or ask product line to measure it with SAR ADC product line.

    Customer need our feedback asap, so your support will be high appreciate. thanks.

    Best Regards
    Iven Xu