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DAC60508: DAC60508MCRTET/MRTE VDD=5.0V, Internal VREF.

Cuong Dao38
Prodigy 90 points
Part Number: DAC60508

I'd like to double check if what is the FS voltage would be when VDD = 5.0V, Vref = 2.5V  (Internal) (DIV=1) and Gain = 2.

Here is the circuit I have which is the same as the evaluation board. 

Thanks,

-CD

  • 0
    TI__Mastermind 25563 points

    Hi CD,

    The FS output would be 5 V for your conditions. 

    A 2.5-V reference with 5-V VDD is near the edge of reference divider conditions:

    Make sure the reference stays at 2.5V or below to avoid the reference buffer shutting down as talked about in this section:

    Best,

    Katlynne Jones 

  • 0 in reply to Katlynne Jones
    Prodigy 90 points

    Katlynne,

      Thanks for your quick response.  
       I'm going to use the internal Vref, so how would I guarantee that the Vref  not exceeding 2.5V?  Would it be better to use an external Vref?  

      Thanks,

    -CD

  • 0 in reply to Cuong Dao38
    TI__Mastermind 25563 points

    Hi CD, 

    In this case, I'd revise my statement to say - make sure your VDD does not dip below 5V to avoid the risk of the reference buffer shutdown. Use the recommended bypass capacitors to ensure a clean supply. It looks like your schematic has them included already. The internal reference has a very good initial accuracy and low drift, so this shouldn't be an issue. 

    Best,

    Katlynne Jones 

  • 0 in reply to Katlynne Jones
    Prodigy 90 points

    Katlynne,

        How much head room do I have or it's absolutely nothing at all, would 4.99V or 4.98V work at all ?  I run out of room to put in a 5.5V regulator.

         I'm open for suggestion for a different part if you have any.  

    Thanks,

    -CD

  • 0 in reply to Cuong Dao38
    TI__Mastermind 25563 points

    Hi CD,

    I am checking with the designers to see if they can give me a more confident answer, but it wont be 4.98V. It should be closer to 10s of mV or more.

    Best,

    Katlynne 

  • 0 in reply to Katlynne Jones
    Prodigy 90 points

    Katlynne,

        I think I should mention this: the 5V supply is 5V+/-5%, so it would deep down as low as 4.75V.  It's best to try with the evaluation board but I don't have one. Would this is something you could try out for me?

    Thanks,

    -CD

  • 0 in reply to Cuong Dao38
    TI__Mastermind 25563 points

    Hi CD,

    I have the DAC80508EVM which is the same device with a higher resolution. I was actually able to lower VDD to below 4V before the reference buffer shut off and the output went to 0V. There are a few comments about this though:

    This is not guaranteed to be the case across all temperatures or conditions which is why they recommended operating conditions table has the margin built in. I would recommend that you get an EVM so you can perform some more tests based on your systems requirements. I wouldn't expect 4.75V to be an issue, but you would have to test to be sure.  

    Second, the full scale voltage is 5V with the 5-V VDD and 2.5-V internal refence. If the VDD goes below 5V then the full scale output voltage will be limited by VDD. For example, if the VDD is 4.75V then the DAC outputs will be 4.75V for any code above 0xF8D or (3891 = (4.75/5)*2^12).

    Best,

    Katlynne Jones

  • 0 in reply to Cuong Dao38
    Prodigy 90 points

    Katlynne,

       Thanks for trying it out on the EVM. 

       For our application, most likely we don't need to generate any outputs that's higher than 4.75V.

       Thanks,

    -CD