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Interfacing DAC714 with PIC24F..

Christian Rückl
Intellectual 340 points
Other Parts Discussed in Thread: DAC714, DAC7731, DAC8560, OPA211, OPA188, DAC8311, DAC8411

Hi,

I'm very interested to use the DAC714 for 0 to +10V operation in my application. The µC there is a Micrichip PIC24FJ64GA004.

I have there one special question with the /A1, update signal. In the application bulletin "

INTERFACING THE DAC714 TO
MICRO-CONTROLLERS VIA SPI"

It is mentioned to tie the CLK to GND potential for continuous data shift and connecting the Chip-Select or Slave-Select Signal to A1 to start the updating.

When I follow this recomondations, does it work with a /SS or /CS signal when it is during data shifting low and after it, changes to high? I cannot produce a short cycle low ss or CS signal after data shifting.

Thanks for answers!

Christian 

  • 0
    TI__Genius 10615 points

    Hi Christian,

     

    Apologies for the delay. I have not used this device before. As I understand from the document and the DAC714 datasheet.

    When /CLK = GND, you can use:

    A0 as a Shift register.

    A1 as an Update.

     

    You can refer to figures 9a and 9b in the DAC714 datasheet.

    The falling edges of A0 shift data into the register.

    After all the data is shifted in, a falling edge of A1 will update the DAC.

     

    If you can share some oscilloscope captures of your digital sequence, I can check if the setup is correct.

  • 0 in reply to Eugenio Mejia
    Intellectual 340 points

    Hi Eugenio,

    At the moment, I'm in the conception state of the project, therefore it is not possible to share any diagrams now - now hardware available yet :)

    But, the important part for updating the DAC is a falling edge on A1 when A0 is the data line and CLK is tied to gnd? Or is it the rising edge of A1?

    There are any specifications of A1 minimum low time for the update pulse?

    Another question:
    I want to use this DAC in 0 to +10V mode. Can I supply on the -Vcc-pin GND potential and on +Vcc +15V? Which things I need to do to use the DAC in this mode? I saw only in figure 6a a diffrent circuit for offset and gain adjustments. Is it only necessary to let the RBPO (Pin11) unconnected?

    Below the schematic around the DAC714 - can you verify if this would work?

    Thanks
    Christian

  • 0 in reply to Christian Rückl
    TI__Genius 10615 points

    Christian,

     

    c.rueckl said:
    the important part for updating the DAC is a falling edge on A1 when A0 is the data line and CLK is tied to gnd? Or is it the rising edge of A1?

    A falling edge on A1 updates the DAC.

    A0 is NOT the data line. A0 is the new CLK line.

    SDI is the data line.

     

    c.rueckl said:
    There are any specifications of A1 minimum low time for the update pulse?

    Take a look at the diagram table on page 4 of the DAC714 datasheet.

    The timing specs A1S and A1H, specify that A1 must remain low for at least 50ns for the update to be valid.

     

    c.rueckl said:
    I want to use this DAC in 0 to +10V mode. Can I supply on the -Vcc-pin GND potential and on +Vcc +15V? Which things I need to do to use the DAC in this mode? I saw only in figure 6a a diffrent circuit for offset and gain adjustments. Is it only necessary to let the RBPO (Pin11) unconnected?

    The datasheet does not do a good job at specifying if the setup is valid at VSS = 0V and VCC = +15V.

    I need to order some devices and test it myself in the lab because all of the designers that worked on this device have long since moved on from our team. I will check this for you, but it will take a few of days.

    In order to use the 0-10V range you need to supply an offset voltage at the Offset Adjust Pin equal to -9.75V. Figure 6 accomplishes supplies this voltage by using a high impedance voltage divider.

     

    What specifications of the DAC714 are attractive to your application? Maybe I can recommend something that fits your needs.

  • 0 in reply to Eugenio Mejia
    Intellectual 340 points

    Eugenio,

    Thanks a lot for your support!!! 

    The specs i need to match for the DAC are:

    • Buffered voltage output with a range from 0-10V. If you have an complete solution with an external buffer an an unbuffered DAC it would be also OK.
    • Digital interface must be SPI.
    • Settlingtime <=10µs
    • Resolution 16 Bit

    Br,
    Christian

  • 0 in reply to Christian Rückl
    TI__Genius 10615 points

    Using precision DACs it will be difficult to generate a signal 0 - 10V with a single supply.

    There are two options:

    • Using ±15V supplies
    • or +5V & +15V supplies

    Using the ±15V you can use the following devices:

    • DAC714 - Buffered voltage output
      • It requires an external offset voltage. Either another supply or a resistive divider.
    • DAC7731 - Buffered voltage output
      • Has internally matched resistors to generate a bipolar or unipolar output.

    Using the +5V & +15V supplies you have a few more options:

    • DAC8560
      • Can produce a 5V output. Needs a gain stage.
    • OPA188 or OPA211
      • Can be used as a gain stage.
      • Has enough slew rate to swing from 0V to 10V in <10us with a +15V supply.

     

    If you have any preferences, let me know and we can tune the parts to your applications.

  • 0 in reply to Eugenio Mejia
    Intellectual 340 points

    Hi Eugenio,

    it looks like that we will go to use the DAC8411 or maybe we reduce a part of the safe-accuracy-overhead and use the DAC8311 (14Bit). The analog output of these devices are up to +5V and need also a gain stage. Can you give me a recomondation for a OpAmp. Would you recommen the same as before: OPA188 or OPA211?

    Thanks again!

    BR
    Christian

  • 0 in reply to Christian Rückl
    TI__Genius 10615 points

    Hi Christian,

     

    Yes. I would still recommend.using OPA188 or OPA211. They have great specifications for input offset voltage, input bias current and low noise. They should also be able to meet your slew rate requirements.

    If you even need a schematic or layout review, or any other assistance please let me know. I would be more than happy to help you with any problems.