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DAC8831EVM troubleshooting help

martha.mogollan
Prodigy 20 points
Other Parts Discussed in Thread: DAC8831, DAC8831EVM

Hi everyone! I'm using a DAC8831EVM with a Spartan 3E. I have already connected SPI lines: SCLK, SDI, CS, LDAC. I have check on the oscilloscope that the Spartan 3E generates a correct SPI signal, and the datasheet of the DAC8831 aproves a digital input high from minimus 2.1V, so my Spartan gives signals from 3.3. V.

Also have DGND to Spartan GND

I apply the voltage supply on the DAC8831EVM J3: +5V, and +5V, -5V, and GND.

I have my LDAC signal from Spartan, so W3 is 2-3

I left the default Vref, so W1 is 1-2

I have an SPI data of hxFFFF, for test

    And when I select SW1: Uni: I have a Vout of 0 V

     When I select SW1: BiPolar, I have a Vout of -2.5V

C1: SDO, C2:SCLK, C3:CS, C4:Vout

What am I missing?? Is there an other line of the DAC8831 that I should consider??

Thanks alot for your advices

  • 0
    TI__Mastermind 46290 points

    Is LDAC grounded in this setup? Your capture does not show what is happening to the LDAC signal.

  • 0 in reply to Kevin Duke
    Prodigy 20 points

    Hello Kevin,

    Yes LDAC is grounded by a switch in my Spartan. And also I have tried with jumper W3 at 1-2 to ground it at the DAC8831EVM.

    Well, I tried with another FPGA board: the Spartan 3, that has an I/O connector nearest of the FPGA chip, and it works better, I already have a great ouput signal of +2.5 V with my 0xFFFF input data :-)  It seems that the other FPGA board give out a too much noisy signal or maybe a glitch or something that the DAC8831EVM couldn't read as input data.


    Thanks a lot


    Do you have any suggestion about how could I reduce de noise on my signal that gives my other FPGA board?

  • 0 in reply to martha.mogollan
    TI__Mastermind 46290 points

    Martha,

    Sometimes adding a simple termination resistor helps, something like 33 ohms. Other times you need to add the complete RC scheme. First, though, I would suggest you try to improve the GND connection between the two boards. A bad GND can add noise to digital signals like this.