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TAD5242: Design for unbalanced and balanced output concurrently

Hakan Lindestaf
Prodigy 20 points
Part Number: TAD5242
Other Parts Discussed in Thread: TAC5242, , TAD5212, TAC5212

Tool/software:

I'm looking to use the TAC5242 in a new design connected to a Raspberry Pi over I2S. In my design I need both unbalanced and balanced outputs concurrently, I don't want the user to have to choose (with jumpers), but have both active at the same time. Preference would be to have standard 1Vrms lineout on the unbalanced output, and professional level +4 dBu on the balanced output, two channels (stereo). Sound quality is more important than cost at this point, however PCB real estate is limited, so using an active opamp for the output may be the best option (dual channel if available). Also I only have 3.3V power supply available.

Thanks,
/Hakan

  • 0
    TI__Expert 3995 points

    Hi,

    Is it possible to maybe share a block diagram of how the end system is expected to look like? With both the connections from Raspberry Pi, and the connections on the Codec's input/output connections?

    Thanks and Regards,

    Lakshmi Narasimhan

  • 0 in reply to Lakshmi Narasimhan Badrinarayanan
    Prodigy 20 points

    I don't have a drawing, but basically the Raspberry Pi has a I2S port (using 3 pins) that will output audio data. I will connect that to the TAD5242, configured for I2S, and then I will have a balanced audio output for connections to mixer boards, and an unbalanced audio output at line levels to connect to standard audio equipment. I don't want any configuration changes (jumpers or software) where the user has to select which output, I just want them to plug in the equipment they have and receive high quality audio.

  • 0 in reply to Hakan Lindestaf
    TI__Expert 3995 points

    Hi,

    When using the TAD5242, the two output pairs (OUT1P/OUT1M, and OUT2P/OUT2M) can be configured together to provide differential, or single-ended output. Based on the MD5/MD4 pin configurations, both OUT1 and OUT2 can be configured as differential or single-ended. (Table from section 6.3.4 of datasheet)

    However, the device doesn't allow to configure OUT1 as differential and OUT2 as single-ended, or vice-versa.

    The TAD5212, which is an I2C-controlled DAC, allows to configure OUT1 and OUT2 independently through I2C register control.

    Thanks and Regards,

    Lakshmi Narasimhan

  • 0 in reply to Lakshmi Narasimhan Badrinarayanan
    Prodigy 20 points

    Thanks, but as I stated in my post I need to output unbalanced and balanced simultaneously, choosing one or the other via the MD pins or I2C on a different chip won't solve my problem.

  • 0 in reply to Hakan Lindestaf
    TI__Expert 6050 points

    Hi,

    Unfortunately, the TAC5242 can only support differential output OR single ended output. Lakshmi was saying that the TAC5212 does support sending differential out one output and single ended out of the other. This table in the datasheet shows the available output settings for TAC5242 (sorry, I see above that Lakshmi sent a similar one too):

    For your application, maybe you can use the second setting here, where it would support either headphone load or line out, or just the differential line out setting (the first option here). You should not have issues with connecting a mono single ended input to the differential output as long as you connect one output to the output common mode and one to one of the two signals of the differential pair. This can be your "unbalanced" line. The main difference between the expected differential output and using one of the lines in the pair would be expected dynamic range - since you would be comparing to a common mode DC signal instead of the second differential output, it will be 0.5x the output amplitude (~6dB lower).

    Let me know if you need more help with this.

    Best,
    Mir