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PCM1774: PCM1774 schematic validation for Line output audio

Jabrane Chakroun1
Intellectual 260 points
Part Number: PCM1774

Hi,

I am using the PCM1774 audio DAC for a wearable device and I would like to confirm the schematic for Line output instead headphone.


- Do I need to add a resistor of 10K to the HPOL and HPOR for impedance matching because the RL=10k instead 16Ohm for the headphone ?

- Is it good to use 2 separate power supply to feed the analog and the digital part of the chip ? in my case I am using the 3.3V for digital and 3V for analog

- Is there any problem to use SAI instead of I2S ?

  • 0
    TI__Guru 52663 points

    Hi Jabrane,

    1. You do not need to add the 10kΩ for impedance matching.

    2. Generally it is best to provide a low noise analog supply.  If your 3.3V is low noise, you could connect them all to the same supply.

    3. My understanding is that SAI modules in processors have I2S support.  The device only supports I2S inputs (as opposed to DSD).

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    Intellectual 260 points

    Hi Paul,

    We will connect a speaker directly to HPOL and HPOR instead of a headphone jack

    1. according to ST reference design they are adding extra resistor as shown below with a value of 30Ohm and 40Ohm

    2. I would like to get an Fc of 20hz for the high pass filter. Is there any formula to change the resistor value as putted in the data sheet to get this frequency ?

    3. I am afraid from sudden noise problem or artifact. Do I need any extra circuit to prevent getting any kind of noise other than adding a capacitor

    Many thanks for your help,

  • +1 in reply to Jabrane Chakroun1
    TI__Guru 52663 points

    Hi Jabrane,

    2. The FC would be determined by the impedance of the speaker and the series resistance as well as the capacitance.  Otherwise it is just an HPF (fC = 1/(2×pi×R×C).

    3. The most common causes of clicks or pops are from clock errors and during startup and shutdown.  Generally, the only to fully deal with them is to implement an external mute device, but that can be costly and hard to detect all fault detection.  You might consider adding the circuitry to your circuit but not populate it until after you evaluate it.

    Thanks,

    Paul