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Original question:

DAC7760: DAC recommendation for wireless MCUs

DAC60004: SLAA869 - adding capcitor to Vref

David__
Genius 3585 points
Part Number: DAC60004

Dear Team

I'm following the design SLAA869 using DAC60004. I have a total of 4 Op Amps to create a uni-polar to bi-polar pulse.

As you see the schematic, initially, I have installed a 180nF capacitor connected to the REF pin for each of the output buffer circuits.

However, previously, I was noticed as;

"It is not necessary to include this capacitor for each circuit. A single 180nF capacitor for the REF pin is sufficient. In fact, there could be some stability risks associated with using 4x."

May I ask why extra capacitors cause stability risks, meaning the stability for the Op Amp?

Since I need to add extra Op Amps with a different DAC IC, I wish to know about this.

  • 0
    TI__Genius 14220 points

    Hi David,

    Thank you for your query. The capacitor at the reference pin doesn't create any stability risk to the op amps as there is a series resistor between the capacitor and the op amp pin. However, one capacitor should be fine for DAC60004.

    Hope that answers your question.

    Uttam Sahu

    Applications Engineer, Precision DAC

  • 0 in reply to Uttam Sahu
    Genius 3585 points

    Thanks.

    Then is this stable for the DAC's REF chip? The VRef 2.5V is provided by the DAC60004.

    I'm curious what is the criteria that one 180nF capacitor is fine when I'm using 4 channels.

  • 0 in reply to David__
    TI__Mastermind 46290 points

    David,

    Unfortunately it doesn't look like the datasheet specifies a maximum capacitive load for the REF pin, but the EVM uses a 10uF || 1uF capacive load on REF, so your proposal of 4 180nF capacitors shouldn't be any issue. I do not believe the 150nF capacitor is a requirement for stability, but just a noise recommendation.

    I will double-check what I can find behind this.

  • 0 in reply to Kevin Duke
    TI__Genius 14220 points

    Hi David/Kevin,

    I verified this with the design team. The capacitor on the VREFIN pin connects to the internal buffer through a resistor. Hence, there is no general limit on the capacitance on this pin. Any value less than 10uF should be fine.

    Hope that answers your question.

    Regards,

    Uttam

  • 0 in reply to Uttam Sahu
    Genius 3585 points

    Thanks, Uttam!

    Uttam Sahu said:
    Any value less than 10uF should be fine.

    Before closing this, may I ask why is shouldn't exceed 10uF?

  • 0 in reply to David__
    TI__Genius 14220 points

    Hi David,

    There is no specific limit on the cap. But we have checked 10uF on the EVM. So, I would recommend to limit it to this value.

    Regards,

    Uttam