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DAC8871: Reference sink, source current.

Ryuji
Guru 20090 points
Part Number: DAC8871

Hello,

I have the question about DAC8871 reference input.
In the datasheet P.16 , there is the description as the following.

"The reference input appears as a varying load to the reference. If the reference can sink or source the required current, a reference buffer is not required."

Could you please let me know the value of sink or source the required current ?
I would like to achieve 1us settling when Vout change from +10V to -10V.

Best Regards,
Ryuji

  • 0
    TI__Genius 14220 points
    Hi Ryuji,

    Thank you for your query. The reference input impedance and capacitance are given on page 3 as > 7.5kOhm and 75-120pF, respectively. You can calculate the DC and AC current requirement if you know the reference voltage. Please note that it will vary with the code due to the ladder architecture. I would recommend using a buffer as it would make your reference circuit simple. Usually, the load regulation of the reference source becomes a concern even though it may be able to supply the current. Please note that the output settling time in an unbuffered R-2R depends on the reference settling during a code switch. Hence, the stability design of the reference opamps is very critical. The feedback capacitor of the opamps will play a very crucial role in this. The more that capacitance, the larger the settling time but the better the stability. Hence, the correct trade-off is required to get the optimum settling performance.

    These values need to be obtained by experimentation or simulation. Unfortunately, the Tina model for this DAC doesn't exist. Hence, I feel experimentation is the best approach.

    Regards,
    Uttam Sahu
    Applications Engineer, Precision DACs