DAC9881: feedback resistor

user5940158

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?

over 3 years ago

0 Akhilesh K over 3 years ago

TI__Mastermind 18546 points

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,

0 Yanni Li over 3 years ago in reply to Akhilesh K

TI__Intellectual 1960 points

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.

0 Akhilesh K over 3 years ago in reply to Yanni Li

TI__Mastermind 18546 points

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,

0 user5940158 over 3 years ago in reply to Akhilesh K

Intellectual 660 points

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?

0 Kevin Duke over 3 years ago in reply to user5940158

TI__Mastermind 46290 points

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.

0 Akhilesh K over 3 years ago in reply to Kevin Duke

TI__Mastermind 18546 points

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,

0 user5940158 over 3 years ago in reply to Akhilesh K

Intellectual 660 points

Thank you very much.

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DAC9881: feedback resistor