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DAC5687: DAC 5687 EVM Board support DC output ?

Part Number: DAC5687
Other Parts Discussed in Thread: DAC5688, DAC5688EVM

Hi,

I am trying to use the DAC 5687 EVM Board to convert 2 x 16bits signals.

to start testing the board I've connected to port A a certain code 0xFFFF but I see nothing on output A.

I disabled all signal processing (bypass all), I am not interested in doing I/Q modulation. I get zero as output.

any advise on how can I see an output voltage corresponding to the the code that I put as input --> basic usage of a DAC.

thanks in advance

sofiane

  • The DAC EVM is configured with a transformer output and will not directly pass DC.  It is intended to pass low IF signals.  If you are using the TSW1400 pattern card, then you can use HSDC Pro to generate a low IF signal and directly test that way.  If you truly need/want DC operation, then you can implement a few solder modifications to bypass the transformers and directly access the differential output lines.  Be careful not to load the board down with 50 ohms or the like as that will impact the signal integrity.

    --RJH

  • Hello,

    Thanks for the fast reply.

    I will not go for the soldering and modifications option.

    Is there another board that can do the job? With more or less same characteristics?

    I saw on a post that the dac 5688 evm can do DC signals.

    I don't know if the output is AC coupled.

    Regards

    Sofiane

  • The DAC5687 (and '88) can do DC signals...it is just that the default configuration is through the transformer.  The primary use case for the high speed DAC is to generate signals in the 10's to 100's of MHz region.  If the primary use case is a static DC output (i.e. not an analog time varying signal centered at 0 Hz) then the '87 device is overkill.  There are other low speed DACs more suitable for that kind of control that you can find on ti.com. If the ultimate goal is to generate a signal in the 10's to 100's of MHz, then the '87 EVM will suffice nicely.  If the goal is to generate a baseband signal of x bandwidth centered at 0 Hz, then the '87 will suffice but the EVM would need the solder modifications to access the differential output directly without the transformer.  If the goal is to interface with a quadrature modulator, then the '88/'87 EVM has that option too.

    --RJH

  • Hello is the DAC5688 output equipped with the transformer? in this case no DC component is possible.

    The signals that I have to handle need a high speed DAC. But it has a slow variation component and sometimes DC. So the DC part is important for me.

    Can I use the DAC5688 without modifications? There is a post where it mentioned that the 5688 can do DC signals. I am wondering if it does it without any modification!

    Regards

    Sofiane

  • Here is the post that I am mentioning.

    If you confirme me that I can use the Dac5688evm to output a DC signal without any modification then I'll purchase one sample.

    Otherwise what type of evaluation board do you advise me to use? Same characteristics than the 87,88...

    2channels,16bits,500MSPS,Parallel interface...

    Thanks for your support

    Sofiane

  • Hello, 

    is it possible to show me how to bypass the transformers ?

    I looked into the schematics there are few resistors and 3.3V supply I don't know from where I can make the modification ?

    thanks in advance

    sofiane

  • The DAC5687EVM is no longer offered on ti.com and I do not readily have the schematics for that EVM.  However, the DAC5688 is on the web and I think that the configuration is the same.  I will use the '88 for this discussion and you should be able to translate these instructions to the board that you have.

    The instructions for the '88 are outlined in section 4.7 of the User's Guide:https://www.ti.com/lit/pdf/slau241.  Specifically, you need to complete the reworks in section 4.7.1 to disengage the modulator and engage the path for the DAC output.  Then you also have to implement the reworks is section 4.7.1.2 to remove and bypass the transformer as well as set the load impedance correctly.  In all, about 20 components need to be touched for both channels.

    --RJH

  • Hello,

    the DAC5687 product is still active, the schematics and all technical documentation can be easily found : www.ti.com/.../DAC5687

    anyways I found the answers to my questions in this document 

    www.ti.com/.../slaa399.pdf

    it mention all needed adaptations to get a DC output.

    Thanks for your reply.

    sofiane