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DAC70004: Software LDAC with LDAC pin issue

Steven Shenker
Intellectual 870 points
Part Number: DAC70004

Hi there,

I have a custom board design where the LDAC pin is permanently pulled down to ground. I had assumed that I could do a "software LDAC" by writing to individual channels using the command "Write to buffer n (IE D27 - D24 set to 0000)", and then finally doing a command "Write to buffer n and update all DACs (Software LDAC) IE D27 - D24 set to 0010" to get a synchronized update of all DACs. Note that I pull the SYNC pin low in between commands (IE after each 32 bits). 

For some reason and maybe my interpretation of the datasheet is incorrect, even after the first command where I only write to buffer N that channel will immediately update its output even before the second command. I do not want this and need to be able to write to individual channel buffers first before doing a synchronized update of all channels with their most recent buffer values. 

Note I have tried setting the LDAC register bits to 1111 to make it ignore the state of the LDAC pin which is always pulled down, but this seems to have no effect. Please let me know if the above operation should ordinarily work as I have intended it to.

 Thanks in advance for your help

  • 0
    TI__Expert 3370 points

    Hi Steven,

     

    Yes, device is behaving as expected and setting SW LDAC to one will allow the immediate update of corresponding channel output (will ignore the LDAC pin).

    In device DAC70004, all the DAC channel will be updated on immediately after the first command if 

      

    1. LDAC pin is tied to zero (low)

    2. or software LDAC bit is set to 1 (high)

     

    and for synchronous update (updating the reg buffer first and then use the SW LDAC bit or LDAC pin to update the channel voltage simultaneously)

    1. use the LDAC pin and make it low (provided SW LDAC bit is set to zero for corresponding channel) 

     

    Hope this information would be helpful.

     

    Thanks,

    Sanjay