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DAC9881: feedback resistor

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Replies: 7

Views: 85

Part Number: DAC9881

I would like to ask the literature about the feedback resistor.It is unclear. Is RFB an internal resistor?On page 26,Note(1) says RFB can be 1kOhm or 2kOhm depending on the gain.that's handled internally depending on a register setting?How to adjust the resistance of RFB?

  • Hi,

    Thanks for writing to us.

    RFB is an internal resistor which will be set according to gain configuration.

    For Gain  = 1 , RFB = 5 Kilo Ohms

          Gain = 2, RFB = 10 Kilo Ohms

    It will be set according to gain settings, you don't need to adjust the same.

    Regards,

    AK

  • In reply to Akhilesh K:

    Could you please interpret how to adjust the an internal resistance according to the gain?

    in addition I want to know the bandwidth of the DAC9881.Thank you very much.

  • In reply to Yanni Li:

    Hi Li,

    If you look ta datasheet pin description, there is GAIN pin which controls the GAIN mode for the device.

    Buffer gain setting.Gain= 1 when the pin is connected to DGND ; Gain= 2 when the pin is connected to IOVDD. Accordingly RFB will be set.

    The GBW product of the internal buffer of DAC9881 is 5.5-MHz typical.

    Regards,

    AK

  • In reply to Akhilesh K:

    Hi AK

    Thank you very much.

    I see the internal buffer you're talking about in figure 64 of the datasheet. Is it possible to know the part number of this specific op amp?

  • In reply to user5940158:

    Hello,

    Just substituting in for AK as the weekend has already begun in India...

    The internal buffer may have initially been based on a pre-existing product design, or an entirely independent design. Even if it were a pre-existing amplifier product, it would have been modified fairly significantly as it were integrated into the DAC design as often segmentation schemes are deployed, especially for high-resolution designs, such that the parameters of the original amplifier would no longer be relevant.

    Do you have a further specific question? Based on what you are seeking to understand, we should be able to come up with an avenue to answer your questions.

    Kevin Duke, MGTS
    ADC Product Marketing Engineer

  • In reply to Kevin Duke:

    Hi,

    Do you need any other help here? It may difficult for us to get the internal parameters of the op amp buffer which is used in DAC9881 due to after-mentioned reasons by Kevin.

    Regards,

    AK

  • In reply to Akhilesh K:

    Thank you very much.

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