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DAC084S085: DAC084S085 full scale output

Kai Nomiyama
Expert 5425 points
Part Number: DAC084S085

Hi team,

I have a question about DAC084S085 full scale output.

In the datasheet, there is description about FSO(Full Scale Output) with 200uA/1mA.
when tested with 800Ω load, Iout=5mA, 5V full scale output, the output voltage is 4.75V.

Is the voltage drop normal operation and why the FSO goes down from 5VA when the output current is increased?

Regards,
Kai

  • 0
    TI__Guru 53663 points
    Hi Kai,

    The DAC's output has an output impedance of 7.5Ω, which would explain some of the voltage drop when the device has enough supply headroom. For example, if you have VA=5V and the DAC output at mid-scale (~2.5V ideally) and drew 5mA of current out of the device, you would see about 37.5mV drop on the output.

    The reason you are seeing a greater drop is that your output lacks any supply margin. If your output is ~5V and the supply is 5V, any current sourcing will force the output to reduce as the DAC output buffer (opamp) cannot drive the current. If you had VREF =5V and VA=6V, you would not see so much of a drop.

    The specification that you are referring to is there to show this behavior, as normal operation (where the output buffer has sufficient supply margin) would show that the output would only reduce by 7.5mV (1mA * 7.5Ω).

    Thanks!
    Paul