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using DAC8811 output to drive op amp based amplifier

anindito santoso
Prodigy 90 points
Other Parts Discussed in Thread: DAC8811, DAC8832

Dear Sir,


Would it be possible to connect the Iout of the DAC8811 to drive op amp based amplifier (either inverting or noninverting amplifier) without using any intermediate op amp which is shown in figure 20 of the datasheet?

What scheme would be the best for such approach?


Kind regards

Anindito

  • 0
    TI__Genius 10615 points
    Hello Anindito,

    Unfortunately, this is not possible. The current output of the DAC is designed to be used with a trans-impedance output stage to convert the DAC current to voltage. I am not sure what you would like to accomplish by supplying a current to the input of an inverting or non-inverting amplifier, since these circuits expect a voltage input, not a current input.

    Can you explain a bit more of the application goals? It will help me understand what you would like to do.

    If you can share some of the specifications from the DAC8811 that are important for your application, I can try to look for a voltage buffered DAC that can do what you want without any more discrete ICs.
  • 0 in reply to Eugenio Mejia
    Prodigy 90 points

    Hi Eugenio,

    I am looking for a fast DAC with a settling time<0.5us based on serial SPI communication. I checked in the product finder and founded that most of the DAC are current output type. I however don't have any space to put an external buffer.

    Could you help me by explaining why I can't use output current DAC pin as voltage output? As it is an R2R configuration I thought the output current pin voltage correlates with its programmed output. http://www.eecs.tufts.edu/~dsculley/RCX/ 

    If you can help me find other DAC which does not required external buffer it will be the best solution.

    Thank you.

    Kind regards,

    Anindito

  • 0 in reply to anindito santoso
    Prodigy 90 points

    Hi Eugenio,

    one more question. In case I use different chip such as DAC8832 which has unbuffered voltage output to drive inverting or noninverting op amp amplifier, would that be possible? And is there any drawback of such a scheme?

    Kind regards,

     

    Dito

     

  • 0 in reply to anindito santoso
    TI__Genius 10615 points
    Unbuffered voltage outputs can only supply a minimal amount of current before their voltage starts to droop. Therefore it is necessary to minimize the current load on an unbuffered voltage.

    An inverting stage loads its input so there would be drawbacks when using it.
    In the other hand, a non-inverting stage would essentially act as a buffer with a gain >1. It won't load the output with anything but the input bias current of the amplifier, which (in most cases) is negligible.
  • 0 in reply to Eugenio Mejia
    Prodigy 90 points
    Hi Eugenio,

    in case the amplifier is a non-inverting, would it be possible to use DAC with current output such as DAC8811 and just connect the current output pin to resistor (one pin of the resistor to current output pin while the other pin of the resistor to ground) to convert it into voltage input for the non inverting amplifier?

    Is there any drawback for such scheme?

    Thank you.

    Kind regards,

    Anindito
  • 0 in reply to anindito santoso
    TI__Genius 10615 points
    Anindito,

    No. The DAC8811 requires an external trans-impedance amplifier. The Iout pin is not meant to be loaded.

    If you can tell me what you would like to achieve I can help you pick the correct DAC.