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Analog volume control with TLV320AIC3206

dnilsson
Prodigy 180 points
Other Parts Discussed in Thread: TLV320AIC3206, TPA3118D2

Hi,

I'm working on a design with the TLV320AIC3206 Audio Codec, this codec will drive a TI Class D TPA3118D2 audio amplifier. While I know that the codec has support for a digital volume control I'd like to add the possibility of using an "old fashioned" potentiometer based analog volume control since the system initially will lack software support for the digital version. The plan is to use the differential interface between TLV320 (output on [RIGHT,LEFT]_LOP and _LOM) and the TPA3118 and to add an optional shunt potentiometer for volume control. My question is regarding the output impedance of the TLV, and also the input impedance of TPA3118, this information is not clear to me from the datasheets. On the output side there is a specification of differential swing into a 10k load in the datasheet, but that doesn't really tell me the output impedance (?). Should the 10k load be intepreted as a single ended or differential load impedance? Same question applies to the TPA3118, is the input impedance shown in table 2 of the datasheet single ended or differential impedance? I assume single ended impedance, is that correct?

Attached is a small sketch of the proposed connection, my headache is to determine the values of the R1-R3 and C1-C2. I assume R1 and R2 are needed to protect the TLV against shortcircuit on "0 volume" setting. DC blocking caps should as far as I can tell also be required, although figure 13 of the TLV datasheet shows a similar application without them (?).

Any input appreciated!

Thanks
Daniel

  • 0
    TI__Guru**** 189401 points

    Hi, Daniel,

    Interesting idea. But, the AIC3206 needs to be programmed at start-up, so why not just make use of the volume control inside the device?

    I have asked my colleague to comment on the impedances.

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 180 points

    Hi Don,

    A bit more on the "why" aspect... I'm building a prototype for a networked audioplayer that can support multiroom audio, it will be using embedded Linux and this HW design will be in the form of a "cape" for a BeagleBone ARM board. So yes, there will be software involved for programming the chip (existing Linux driver). Since this is an embedded system without graphical user interface the challenge is to provide feedback on what the volume is set to when using the digital volume control. Of course this can (and will) be implemented using an LED bar or LCD display with supporting software on Linux, but I was hoping to not have to implement that on the first prototype.

    Looking forward to hear from your colleague.

    Thanks
    Daniel

  • 0
    TI__Genius 12255 points

    Hi

    In fact , we usually use the circuit like below:

    The first block is used to volume control through change the resister R(the one connect to the ground).

    The second block is used to filter the high frequency noise.

    The third one is the DC block

              

  • 0 in reply to Derek Xie
    Prodigy 180 points

    Hi,

    Thanks for the input. Is that example circuit above per channel (i.e. differential input mode) or is the example shown for a single ended input configuration?

    Regards

    Daniel

  • 0 in reply to dnilsson
    TI__Genius 12255 points

    Hi 

               This is for Tpa3118 differential input. 

                If you want to use single ended input configuration, see the picture below:

                Cut off one input from the AIC3254 and connect to the GND. 

               

  • 0 in reply to Derek Xie
    Prodigy 180 points

    Thanks, I think I have the input I need now to move on with my design.