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DAC60508: DAC Output Range Configuration

Zeev Gerber
Intellectual 310 points

Part Number: DAC60508
Other Parts Discussed in Thread: DAC80508, TLV431

Tool/software:

Hi,

why I see in the data sheet of the DAC60508 that DAC Output Range Configuration is not recommended to use with DIV Setting = ÷1 and GAIN Setting = X1.

regards

Zeev Gerber

  • 0
    TI__Guru** 100785 points

    Zeev,


    The answer to this post can be found in the following post (the post describes the 16-bit DAC80508 instead of the 12-bit DAC60508 but still applies):

     https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/844638/dac8568-dac80508-setting-div-1-gain-1-are-not-recommended-why 

    The performance of the resistor ladder in the DAC is better with additional headroom from the internal reference voltage when you set the DIV=÷2 and GAIN=×2. This should give the same output of 0V to VREF as the DIV=÷1 and GAIN=×1.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Intellectual 310 points

    Hi,

    could I work with DIV=÷1  if my VDD is a little under 5V? 4.75V for example? 

    without reference buffer shut down which make the output zero.

    Zeev Gerber

  • 0 in reply to Zeev Gerber
    TI__Mastermind 42253 points

    Hi Zeev, 

    Copying your other questions here: 

    I want to work with voltage output of 5V with VDD of 5V.

    The VDD is not promised to be over 5V and could be a bit under this value (could be 4.75V).  

    what is the value the reference divider issues a reference alarm condition and set the output to zero?

    I didn't have a problem to work with the range of 0V to VDD if VDD is above 4.75V.

    ----------

    I want to drive multiple (4) dac's (dac60508) with one voltage reference (tlv431).

    the dac60508 drive the reference as output when working with internal reference which is the default.

    how to handle the voltage contention between the dac's and the external reference and between the dac's also, until I configure the dac's to work with external reference?

    in earlier question, I see TI recommended on series resistor between the reference of ~100ohm.

    should i use 4 resistors in this case? one per dac reference pin?

  • 0 in reply to Katlynne Jones
    Intellectual 310 points

    Hi,

    do you have answers for me?

    zeev gerber

  • 0 in reply to Zeev Gerber
    TI__Mastermind 42253 points

    Hi Zeev, 

    The designer let me know that the reference headroom is worst at extreme cold temperature. The data given in the datasheet is specified across the entire temperature range, so it is a bit more conservative if you are running near room temperature. This is why you see no issue with 4.75V VDD. I checked and I don't have any data that shows the exact requirement at different temperatures. 

    One resistor for the four devices is fine. The voltage on the DAC side of the resistor will be fixed at ~2.5V and the same current will flow through the resistor until you are able to power down all four references. You could pull the CS of all four devices low at the same time and send one command to disable all VREFs at the same time.

    Best,

    Katlynne Jones