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How to distribute audio signal from DAC

Discussion in 'Audio' started by kruskal, Mar 24, 2017.

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  1. kruskal

    kruskal

    22
    0
    Jan 27, 2017
    I have a STM32F410 running at 3.3V. The uc has a DAC that according to the datasheet is able to supply max 25mA. The output signal should be routed to two different receivers in my circuit, each with an input resistance of 150k ohm.

    Are there any precautions to take when distributing an analog signal to multiple receivers? Or can I simply just wire the signals together? Current wise I don't see the need for any buffers..

    Out of curiosity, is it only the DAC current that limits how many receivers I can have in a circuit, as shown below?

    dac-split.png
     
  2. AnalogKid

    AnalogKid

    2,337
    654
    Jun 10, 2015
    What are the "receivers"?
    Do then have input coupling (DC-blocking) capacitors?
    Are they located on the same board as the DAC? If not, then shielded cable should be use for the interconnect.
    Check the uC datasheet. You might be citing the pin's output current capability when acting as a digital output rather than as an analog output.

    ak
     
  3. kruskal

    kruskal

    22
    0
    Jan 27, 2017
    Thanks for the reply AK.

    The receivers are two identical IC's located on the same PCB, ~30mm trace from the DAC pin.

    Not as of now. The typical application in the datasheet for this IC states that AC decoupling capacitor, 0.1uF, are optional, so I can of course add that. Should I?

    You are probably right, 25mA is stated as the max current output of any GPIO pin. But I can't really find any max current rating for the DAC output. Here are a snippet of the DAC electrical characteristics:
    stm32f410_dac_characteristics.png

    (2) is "Guaranteed by design."

    It seems the DAC has an internal output buffer as well. My interpretation of Rload is that the DAC should behave as specified as long as the total resistance (to GND) is above 5k ohm. Is this a correct assumption?

    So with two IC's with 150k ohm input resistance each, the total parallel resistance seen by the DAC is 75k ohm, which means that it is safe to connect the DAC directly to the two IC's?

    If my assumption is correct, it should in theory be ok to connect up to 12 receivers with 150k ohm input resistance as this will give a total resistance of ~7k ohm.
     
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