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DAC8871: Reference input

Dukel
Intellectual 610 points
Part Number: DAC8871
Other Parts Discussed in Thread: OPA2277,

Hi all,

Is it also possible to just connect a ±18V or less power supply to the VrefH and VrefL instead of using an OPAmp like the suggested in the datasheet (OPA2277)?

If this is possible it would still be important to use the 10uF and 1uF capacitors right?

Best regards,

Dukel

  • 0
    TI__Genius 14220 points
    Hi Dukel,

    Thank you for your query. The accuracy of the DAC depends on the reference. That's the reason in unbuffered DAC's, the reference inputs are configured in force-sense mode so that the reference is accurate till the internal R2R ladder. This makes sure the parasitic RLC's from the pin to the ladder are compensated by the opamp feedback loop.

    It is possible to just use the FORCE pins of VREFH and VREFL to provide an external reference. As long as the source is a stable reference source, the accuracy will be somewhat maintained (internal parasitics will not be compensated). However, if you use a power supply as the reference source, the accuracy of the DAC will be heavily degraded. Hence, We would not recommend a circuit like that.

    Regarding the decoupling capacitors, it is recommended to use a bulk and a high-frequency capacitor close to the power supply pins in order to minimize the switching current loop.

    Hope that answers your question. If you still have doubt about chossing the right part or the accompanying circuit, please let us know your requirements in detail. We will be glad to support.

    Regards,
    Uttam Sahu
    Applications Engineer, Precision DACs
  • 0 in reply to Uttam Sahu
    Intellectual 610 points

    Hi Uttam,

    Thank you for your reply.

    I already have the DAC8871 and first want to test it. I want to use the myDAQ's ±15V as reference.

    Would it be ok to connect like this, just for testing. later on I will use the recommended reference schematic.
    The capacitor wil be one 1uF and 10uF parallel. 

    Best regards

  • 0 in reply to Dukel
    TI__Genius 14220 points
    Hi Dukel,

    The SENSE is not an input pin - it's an output pin from the DAC. For your testing, use +15V to VREFH-F and -15V to VREFL-F. Leave the VREFH-S and VREFL-S open.

    Please note that the respective FORCE (F) and SENSE (S) pins are shorted to each other internally.

    Regards,
    Uttam
  • 0 in reply to Uttam Sahu
    Intellectual 610 points
    Hi Uttam,

    I just saw that I made my drawing wrong. What I wanted to do was indeed +15V to VREFH and -15V to VREFL and the VREFH/L-S to 0, but you now say leave them open so because their outputs, so that is what I'll do.

    thanks for your help!