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TLV320AIC3106 differential to single ended

Daniel Van Veen
Prodigy 60 points
Other Parts Discussed in Thread: TLV320AIC3106

Hi all,


I'm currently designing a board that utilizes the TLV320AIC3106. The requirement is to have the ability to provide line in/out in either differential or single ended mode without a board redesign. The inputs are fine, I route the differential line inputs (by way of an AC coupling capacitor) directly to the IC from a 3-pin XLR. When used in single ended mode, the LINE_M pin is grounded in the cable. Selecting single ended mode on the IC will disconnect this line anyway. In differential mode it is left as is.

I can't seem to find any information on whether or not the differential line outputs can be configured in single ended mode (i.e. Mono_LOP passes the signal and is internally referenced to ground). Does the chip have this capability or do I need a differential line receiver to convert from differential to single ended?

Thanks for your help.

  • 0
    TI__Genius 9175 points

     Hello,

    I don’t think the part is internally configurable for single ended line out applications. Trying to configure it at the board level by referencing one side of the differential pair to ground will halve the available signal swing.

    Regards,

    Matt

  • 0 in reply to Matthew Beardsworth
    Prodigy 60 points

    Thanks Matt, I'll include a differential op-amp for converting to single ended.

  • 0 in reply to Matthew Beardsworth
    Prodigy 20 points

    Matt,

    You wrote: "Trying to configure it at the board level by referencing one side of the differential pair to ground will halve the available signal swing."

    I just stumbled across this post, and I've been looking for the same info. Can you confirm that the line outputs on the 3106 *will* work as single ended, assuming one is willing to accept half of the specified voltage swing? We've done that with other AICs, but either it's not working with the 3106 or we're doing something wrong. We have 4 of these parts in a design and have just taken the line out + pins as single ended outputs referenced to ground. They feed a simple op-amp buffer. The problem is we're not seeing the signal we expect - it's distorted (almost like it's clipped) and placing any load on the output to ground kills the signal. I see that the 3106 datasheet says nothing about using the line outputs in single-ended mode, so perhaps this part doesn't actually support that?

    I'd appreciate any input, as well as confirmation that single-ended mode should work with the line outs on the 3106.

    Thanks,

    Doug Hall, Raleigh NC

  • 0 in reply to Doug Hall
    TI__Genius 9175 points

    Hi Doug,

    This part does not support single-ended line out. Grounding one side of the diff stage output will case that leg of the stage to hog the source current. Therefore, grounding one output will re-bias the other output in an unusable state and may even cause a DC offset due to unbalanced current.

    Differential outputs don’t play nice like inputs do.

    Since you have an op-amp buffer, you can used a difference amp instead, to buffer and act as a differential to single ended converter.

    Regards,

    Matt

     

  • 0 in reply to Matthew Beardsworth
    Prodigy 20 points

    Thanks, Matt. Just to confirm, we're not grounding one side of the differential pair. We're just taking the output from the line out + (referenced to ground) and leaving the line out - disconnected. We've seen that done successfully on some other AICs (such as the AIC23) and thought that the 3106 would behave the same way. No? I can certainly understand how grounding one side of the pair would be problematic, but we're not doing that.

    Thanks for your help.

    Doug

  • 0 in reply to Doug Hall
    TI__Genius 9175 points

    Hi Doug,

    Sorry, I miss understood your setup. I understand it now.

    The only reason that I can think of for your issue is that this part does not have a ground referenced output stage internally. Instead the output floats at Vcc/2 or something similar. Therefore, a ground reference will cause large DC currents and mess with the biasing.

    I do not have one of these EVM’s on hand to test, but with the part active, you can measure the DC voltage on the +/- lineout legs to ground with no additional load to see if there is a significant offset. If there is, the part is not ground referenced. In this case you would need to add a DC blocking cap on the output leg or switch to full differential output.

    Regards,

    Matt