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DAC7551: Output impedance (min/max)

cafain
Mastermind 6365 points
Part Number: DAC7551

Hi,

Let me ask about the output impedance of the DAC7551.
Data sheet (SLAS441E) "DC Output impurity" is regulated on page3.

① The regulation value is only the typical value of 1Ω. Please tell me the min and max values.
　　(It is fine also for reference value)

② Does the output impedance vary with frequency?
　　If it fluctuates, what percentage will it be?

best regards

  • 0
    TI__Genius 14220 points
    Hi,

    Thank you for the query. You can find a related answer in this post:

    e2e.ti.com/.../456662

    I don't think the output impedance will vary with frequency. Let me confirm that with the design team. I will get back if it is not so.

    Regards,
    Uttam Sahu
    Applications Engineer, Precision DACs
  • 0 in reply to Uttam Sahu
    Mastermind 6365 points

    Hi,Uttam-san

    I appreciate your early reply.
    Please access and check the address you taught.

    It is an additional question.
    Please tell me how to measure 100kΩ of "Reference input impedance" of DAC7551.(VREF-L)
    (If you have a measuring circuit, please tell me about it)

    I also need to experiment and confirm.
    best regards

    Cafain

  • 0 in reply to cafain
    TI__Genius 14220 points
    Hi Cafain-san,

    First of all, sorry that I missed your name in the link I sent you. I got the answer from the design team for your questions. They are as follows:

    1. For question 1. on the reference input impedance, it could vary relative to the SiCr thin film resistor specification from fab. That would be up to +/- 20%. For the DAC output impedance, it is harder to say. In most cases the VOUT feedback connection is made on the layout at the pad, hence, the VOUT output impedance would be quite low. Typically we specify 1 ohm as there will be the wirebond but even that is quite low. So it could be less than 0.5 ohm possibly. At DC levels we would not expect it to go over 1 ohm with the assumption that the feedback is made at the pad.

    2. As for frequency dependence, the VOUT output impedance will go up as the open loop gain of the op amp drops vs. frequency. However, there is not much data on this.

    3. For impedance measurement: We normally use a current sense resistor between the reference source and the VREFH or VREFL pin, and measure the voltage drop across it

    Regards,
    Uttam