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DAC8564: DAC8564:

Bhaktprakash Patel
Prodigy 70 points
Part Number: DAC8564

Hello

I have (5) DAC8564 on one PCA design. I AVdd is 5V, and VioVdd is 3.3V. See image below. 

I am having difficulty getting the DAC's to use an external  4.096V Vref. I have disconnected the 4.094V source, until I can prove the internal Vref has been powered down. I bussed all the Vref DAC pins together, and have sent (via SPI) the following bits:

  • nEN1 = 0, nEN2 = 1          0x012000             Disable U1 DAC Vref
  • nEN1 = 0, nEN2 = 1          0x412000             Disable U7 DAC Vref
  • nEN1 = 0, nEN2 = 1          0x812000             Disable U9 DAC Vref
  • nEN1 = 0, nEN2 = 1          0xC12000             Disable U10 DAC Vref
  • nEN1 = 1, nEN2 = 0          0x012000             Disable U11 DAC Vref 

After the above SPI commands have been sent, I still see Vref as 2.5V. I have checked timing, voltage levels, no signal ringing, clock edges, all looks good.

I have not even send any DAC vales after the above commands have been issued - still Vref = 2.5V !!!! 

Just for my knowledge, if the above had worked, does bit DB13 always have to be "1" going forward while sending DAC values so that the internal Vref is OFF?

     Thanks

  • +1
    TI__Mastermind 33348 points

    Hello,

    No, bits 15 to 0 are the 16 data bits when you are writing to update the DAC. DB13 only disables/enables the internal reference when the control bits 23 to 16 are set in the case I highlighted below:

    You are measuring the 2.5V on the VREF output pin? The data you have written looks correct. Can you share a oscilloscope shot of one of the write sequences so I can also verify the timing?

    One additional comment, it looks like the A0 and A1 pins of U11 are connected to IOVdd but you have it listed as 00. Maybe this could be the issue especially if you have all the VREF pins tied together. Maybe this one is not getting updated correctly. 

    Best,

    Katlynne Jones 

  • 0 in reply to Katlynne Jones
    Prodigy 70 points

    Hello

     Thanks for your support. It now works, it was due to "A0 and A1 pins of U11 are connected to IOVdd but you have it listed as 00" - once we wrote the correct " 0xC12000" to U11, Vref is low and I now we can drive 4.096V into the DAC.