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Original question:

DAC80502: Is there any setting that needed to be done when switching to the external VREFIO

DAC80502:About using an external reference

Taroimo
Intellectual 680 points
Part Number: DAC80502


Dear TI team

 

I have a question related to the content of the thread below.

https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/1000627/dac80502-is-there-any-setting-that-needed-to-be-done-when-switching-to-the-external-vrefio?tisearch=e2e-sitesearch&keymatch=DAC80502#

 

I believe the "DAC80502" uses the internal reference voltage of 2.5V by default.

So I am aware that when using the "REF5050" as an external reference, I need to use the SPI command to change the mode from INT to EXT.

At this time, is there any problem if the output of "REF5050" is asserted before changing the reference mode from INT to EXT?

 

Best Regards,

Taroimo

  • 0
    TI__Guru 54643 points

    Hi Taroimo-san,

    The internal reference is enabled by default, so the external reference will be shorted to 2.5V until the reference is disabled.  We recommend a series resistance between the two reference to limit current.  ~100Ω is recommend.  Note that reference input is internally buffered, so this 100Ω does not cause much I×R voltage drop.  The input impedance of the reference input pin is ~100kΩ.

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    Intellectual 680 points

    Hi Paul,

     

    Thanks for your prompt reply.

    We will try to put a series resistor between the two references as you suggested.

     

    However, in the current evaluation, the absolute maximum rating of the "DAC80502" "VREFIO" pin is 5.3V, so I don't think there will be an immediate problem.

    (The DAC80502 VDD is 5V and the REF5050 output is also 5V.)

    Is this perception correct?

     

    Best Regards,

    Taroimo

  • +1 in reply to Taroimo
    TI__Guru 54643 points

    Hi Taroimo-san,

    The primary issue with shorting the two references is that the DAC80502 reference output will sink high current, which causes power dissipation.  It will not necessarily damage the pin or device, but it would mean the external reference will likely enter short circuit condition, and the supply for the reference will have to provide that current.