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DAC7568: How to update all outputs simultaneously without LDAC pin?

Vadim Berdichevsky
Prodigy 60 points
Part Number: DAC7568

Hello,

I am using the DAC7568IAPW device that does not has an LDAC pin. I want to update all outputs simultaneously with software command, but I am not sure how to do it.

I think to use the "Write to Selected DAC Input Register" command to load a word into each DAC channel, and then to use the "Update Selected DAC Registers" command with "Broadcast mode - Update all DAC registers" to update all channels simultaneously with the data that I previously loaded into the registers.

But I am not sure that this is the right way, as in the "Broadcast mode" command there are "Data" bits in the datasheet that are not "don't care" (see screenshot) and I don't understand what this data does. I am afraid it will override the data that I have previously loaded into the registers.

What is the right way to update all channels simultaneously without LDAC pin?

Best regards,

Vadim.

  • 0
    TI__Prodigy 580 points

    Hello Vadim,

    Let me look into this and get back to you. 

    Regards,

    Luis 

  • 0
    TI__Prodigy 580 points

    Hi Vadim,

    That should be the correct way to update the registers. I believe that says data on the picture just to show that the data will be loaded. 

    Another way you can do it too is shown below (Table 4 page 37): 

    Where you can write to a selected register and then update all DAC registers. Which might save you one transmission cycle. This should be used on the last DAC you are updating the data, if all 8 outputs are getting updated then you'd use it when writing to register H.

    Do you happen to have the DAC7568EVM? this can be quickly checked if so. 

    Regards,

    Luis

  • 0 in reply to Luis Brum
    Prodigy 60 points

    Thanks Luis, I am aware of the second way that you suggested, but it is not suitable for my application because I have three DAC7568 devices that share the same DIN and SCL lines (with separate SYNCs). I need to update all 24 channels simultaneously. Therefore, I must at first load the registers, and then to send the update command to all three DACs.

    Unfortunantly, I don't have the DAC7568EVM and I need to send my PCB to manufacturing as soon as possible, so I can't wait for the EVM to arrive.

    It is a little bit strange that the "data" in the picture is just to show that the data will be loaded, because it appears on the datasheet under DB19-DB4, which implies it is data that I have to send as part of the command. But it doesn't say which data should I send. I would expect that the data is "don't care", but I am not sure. I would appreciate if you can check it somehow so I can be sure I can send the PCB to manufacturing.

  • +1 in reply to Vadim Berdichevsky
    TI__Guru 53633 points

    Hi Vadim,

    the "data" in that table is really "don't-care" bits.  That command will only latch the values already stored in the input register.  It will not overwrite the input register.

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    Prodigy 60 points

    Thank you Paul.

    Best regards,

    Vadim.