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DAC8822: DAC8822 Vref/R1x/Rofsx current requirements

Tomasz Czaplinski1
Prodigy 10 points

Part Number: DAC8822
Other Parts Discussed in Thread: DAC8820, DAC8811, OPA140, OPA211

Hello,

I am working on an application which will use couple of DAC converters (2x DAC8822, 1x DAC8820, 1x DAC8811). I was planning one 10V Voltage reference source for all DACs. I was planning to use DAC8820/DAC8820 in the Bipolar output configuration.  In that situation the reference voltage is provided to pins R1x and Rofsx as per p.17 of the following datasheet:
http://www.ti.com/lit/ds/symlink/dac8822.pdf

Also in this datasheet it is stated that R1 pin has 4kOhm min (5k nominal) whereas Rofs has 8kOhm min (10k nominal). With 10V as a refference to the DAC this makes 2.5mA and 1.25mA of current.
My question is - can I simply assume that the current is then maximally 3.75mA per channel / 7.5mA per DAC8822?

If so, the DAC8820 has 2.2mA (1.1+1.1mA each from 9kOhm resistance from datasheet) and DAC8811 has 2mA (5kOhm as per datasheet), which brings me to 7.5mA + 2.2mA + 2mA (DAC8820 and DAC8811 have 1ch only).
This makes 11.7mA in total.
Isn't it too extreme assumption?

I was planning to use REF5010 as 10V Voltage Refference but it can only deliver up to 10mA. Can it be safely used or I should look for something else? TPS7A470x could be an option, as it is an RF LDO voltage regulator, however I do not see noise figures for 0.1Hz to 10Hz, which I suppose will be much higher for this part than REF5010.

Kindly let me know your thoughts and if possible, the suggested solution for this application.
Thank you.

  • 0
    TI__Guru 56933 points

    Hi Tomasz,

    Welcome to the E2E forums!

    Your math is correct, so I think we need to find a solution for the reference current limits. You could consider using multiple references, or you could buffer the reference with a unity gain opamp.  Most precision opamps will have the noise specification you are looking for.  For example, you could consider a low-noise, low-offset devices like the OPA140 or OPA211.

    I am interested to know about this application - do you mind telling me more about it? If you would prefer you can email me directly at frost@ti.com. We can also discuss some future MDAC development on our roadmap.

    Thanks,

    Paul