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DAC80508: Output Load response

Hiroaki Yuyama TED
Expert 1470 points
Part Number: DAC80508
Other Parts Discussed in Thread: DAC81408, SN74LV1T125,

Dear, support Team.

Our customer plans to drive the analog output of the DAC81408 as a power supply for the SN74LV1T125.
The SN74LV1T125 drives a signal speed of 10Mbps and a load of approximately 10mA.
The settling time of the DAC81408 is 12usec, is there any problem with responsiveness of the connected load?
Also, can the DAC81408 output be stabilized with a capacitor?

Best Regards,
Hiroaki Yuyama

  • 0
    TI__Mastermind 33348 points

    Hi Yuyama-san,

    High current output loads will cause a decrease in the load regulation of the DAC80508.

    These figures are from the datasheet. They use a VDD of 5.5V and the following gain selections:

    It looks like a 10mA load might only cause load regulation issues when the DAC code is 0x0000. The output will start to rise above 0V. 

    You can add a capacitor to the output of DAC80508. The maximum capacitive loud is given in the datasheet:

    Going beyond the max could cause output stability problems. 

    Best,

    Katlynne Jones 

  • 0 in reply to Katlynne Jones
    Expert 1470 points

    Hi,Jones-san,

    Thank you for your reply.
    I was able to understand the input code and drive current for the DAC80508.
    I would also note the maximum value of the output capacitor.

    I'm also concerned about sudden changes in output load.
    The output of the DAC80508 has a settling time of 12usec, but can it be tracked?
    I am planning to insert a capacitor to stabilize the output, is this idea correct?

    Best Regards,
    Hiroaki Yuyama

  • 0 in reply to Hiroaki Yuyama TED
    TI__Mastermind 33348 points

    Hi Yuyama-san,

    The 12μs settling time comes from changes in the DAC input code. It's the amount of time the output buffer (op amp) takes to settle after a change on its input (the DAC resistor ladder). The output wouldn't see the same settling time due to a load change, but with that being said, you can use a capacitor to stabilize the output for sudden load changes. 

    Best,

    Katlynne Jones 

  • 0 in reply to Katlynne Jones
    Expert 1470 points

    Hi, Jones-san,

    Thank you for your advice.
    I also understood the settling time considerations of the DAC80508.
    I watch out for oscillations in the output of the DAC80508 and cover the  sudden load changes of the SN74LV1T125 with a capacitor.

    Best Regards,
    Hiroaki Yuyama