ADR444 Incorrect Output Voltage

I am trying to use the ADR444 as a 4.096V reference for the ADAS3023, using the AD8031 as a buffer, as suggested on the ADAS3023 data sheet.  The ADR444 is giving about 4.3V, which is dropping to 4.2V after the AD8031.  Both of these are operating off 5V input.

I don't know that this will be a major issue, but I wonder if it's possible I'm missing something.

  • 0
    •  Analog Employees 
    on Aug 27, 2015 7:08 PM

    Hi David,

    The output you are seeing (4.3V) is already out of spec, since the ADR444 should be within 5mV of 4.096V. Did you include 0.1uF capacitors at the input and output of the ADR444? The datasheet of the ADR444 indicates that these are required.

    Thanks,

    Kris

  • Hi Kris,

     

    Thanks for the reply.  I do have a capacitor on my +5V input, but realized I missed one between the ADR444 and the AD8031.  Luckily I was able to connect one and now my output from both is 4.13.  It's closer now but still out of spec.  Any further suggestions?

     

    Thanks again!

     

    David

  • 0
    •  Analog Employees 
    on Sep 2, 2015 6:03 PM

    Hello David,

    Can you just confirm whether you are measuring the voltage while the AD8031 is connected to the ADR444? If you are, could you disconnect the AD8031 from the output of the reference and measure the output? I just want to check whether it is a problem with the loading of the reference.

    Thanks,

    Kris

  • Kris,

    This seems to have solved the problem!  I have been doing this on a PCB but luckily the AD8031 footprint allowed a 0R bridge directly to the ADAS3023.  Before making the bridge, I was getting 4.096V from the ADR444, and after the connection, I was still getting 4.096V.  Thank you for your help!

    Do you understand what was causing this?  Could it be a bad chip or is it something I should have spotted in the datasheets?  In case you feel like offering more insight, I'm including the original schematic for this part of the board.  The ADR434 is now the ADR444 and it has a 0.1uF capacitor on the output, and +IN and OUT pins of the AD8031 are now connected while the chip itself is gone.

    Thanks again,

    David