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Original question:

ADS1248EVM-PDK

ADS1248EVM-PDK: ADS1248EVM-PDK... IDAC0 is not working. IDAC0 Muxed to Ain2 but no current is available

Michael Black78
Intellectual 350 points
Part Number: ADS1248EVM-PDK
Other Parts Discussed in Thread: ADCPRO, ADS1247, ADS1248

IDAC0 is not working. IDAC0 Muxed to Ain2 but no current is available.

  • 0
    TI__Guru* 95185 points
    Michael,


    Is IDAC1 working or is the current available at other pins?

    One common problem is that the internal reference needs to be enabled to use the IDAC currents. In the ADS1248EVM plugin for ADCPro, go to the Power & Ref tab and enable the internal reference. Then set the IDAC magnitude and make sure the current goes to the proper output.

    If that doesn't work, post back and we'll continue debugging.


    Joseph Wu
  • 0 in reply to Joseph Wu
    Intellectual 350 points
    I am using ADCpro and i know how to use the program.
    I have another board with less analog pins (ads1247) that works fine.
    none of the IDAC is working and i do enable internal reference and set the Idac Magnitute ..
    i have been using the other board (ads1247) together with ADCpro and dont have any issue ....
    the borad that i have issue (ads128) seems to be broken.
    please note that i have 2 MMB3 and also tried to switch the borads and even did firmware uppgrade and it dose not work.

    I have idac Magnitude set for 1000 micro amp
    reference selected Vref0
    VREF: 2.048
    IDAC0 routing (selected AIN)
    under I/O config :
    AIN0= AinP
    AIN1=AinN
    AIN2=IDAC0

    with this setting the 1247 board work and i can see the current go trough rtd and i am able to measure the voltage over the RTD but
    the 1248 board that i bought few days a go do not put any current ..

    i think there is hardware issue with new 1248 board that i just bought
  • 0 in reply to Michael Black78
    TI__Guru* 95185 points
    Michael,


    If you think that this is a hardware issue, then you'll need to return it for an exchange. However, I'd still like to verify that your test isn't incorrectly hooked up and just want to check any functionality on the board.

    How do you have your resistors connected to the board? Can you show a basic block diagram (or even a photo of the setup)? Are you able to collect any data from the board? Making a quick measurement of the temp sensor will give an expected result using the internal reference. Can you make measurements from any of the analog input pins? There are 8 inputs, and you could try to measure a voltage divider from the supply. Are you able to route either IDAC current to any other analog input pin or to IEXC1 or 2?

    Again, if the board is damaged or has some bad connection, you'll need to return it for an exchange. I will say that these boards are tested by the contract manufacturer, and should have been functional when shipped out.


    Joseph Wu
  • 0 in reply to Michael Black78
    Intellectual 350 points
    You are right, it is nothing wrong with the board as I received a new ADS1248 today and it did not work. Please see the attached document in PDF for all details. Please advise on how to move forward.

    Thank You
  • 0 in reply to Michael Black78
    TI__Guru* 95185 points

    Michael,

    The only thing I can think of is that for your connections, you don't have a connection between REF- and ground. If REF- is floating, there's nowhere for the current to sink and nothing will come out of the IDAC. I think this is a difference between the ADS1247EVM and the ADS1248EVM for the REF- connection.

    However, just in case this isn't the problem, I did run a quick alternate test to make sure currents come out of the IDACs. I ran a test with a 1kΩ resistor going from AIN0 to ground. Here's a quick picture of the setup.

    Using ADCPro and the ADS1248EVM plugin, I set the Power & Ref tab. I turn on the Internal Reference, set the IDAC magnitude to 1000uA and then set the IDAC to the AIN pins (both IDACs)

    Then I go to the I/0 Config tab and set IDAC0 to go to AIN0 and IDAC1 to go to AIN4 (I do this to get it out of the way.

    After that, I just measure the voltage across the resistor to verify that the current is there, and I get about 1V across it.

    Again, if the REF-/ground connection isn't the problem, I would duplicate my test to see if you can route the current in this way. I would note that the data taken from the application shown in the datasheet comes from this EVM.

    Joseph Wu

  • 0 in reply to Joseph Wu
    TI__Guru* 95185 points
    Michael,


    Were you able to get the IDAC currents working on your EVM? As I mentioned in the last post, I think this is just a difference in the REFN connection. The ADS1247EVM has a direct connection for REFN to ground while the ADS1248EVM does not.

    I'll close this post for now, but if you continue to have problems, post back and we can continue to debug the problem.


    Joseph Wu