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LM4947: Mixer and Volume control part selection

Alwyn DSouza
Intellectual 360 points
Part Number: LM4947
Other Parts Discussed in Thread: LM49251, LM49250, TLV320AIC3107, TLV320AIC3007, TLV320AIC32

Actually this question concerns three parts

LM4947, LM49250 and LM49251.

I have 1 mono electret condenser microphone input and 2 stereo line inputs, I want to mix combinations of these which I think is possible with the above chips.

My concern is can these chips handle the number of inputs

For LM4947 I see that the input selection has a particular mode

Table 4. Input/Output Control

L2R2 L1R1 SE/DIFF
Select LIN1 and RIN1 Stereo Pair 0 1 0
Select LIN2 and RIN2 Stereo Pair 1 0 0
Select LIN1+LIN2 and RIN1+RIN2 Stereo Pair 1 1 0
Sets Stereo Inputs to Differential x x 1

As seen I don't quite understand what LN1+LN2 and RIN1+RIN2 mode does?

Can I connect 2 stereo single ended line inputs Line1_L / Line1_R and Line2_L / Line2_R to the pins LIN1 / RIN1 and LIN2 / RIN2 and get the requirements done?

Will the other chips LM49250 and LM49251, be better suited for this?

I also see that these chips don't have an inbuilt microphone preamp, any suggestions for a pre-amp chip with minimal external components would be welcome!

  • 0
    TI__Guru* 84915 points

    Hi, Alwyn,

    As shown in the table that you attached, the analog inputs are supported as a single stereo pair (LINx and RINx) or as a mixed stereo pair (LIN1 + LIN2 and RIN1 + RIN2). The mono input is dedicated for the mono output, which cannot be used to be mixed with the line inputs.

    What I could suggest is take a look at the devices below, they have a more complex mux and mix that can be used for all the analog inputs. They can be then routed to the analog outputs.

    TLV320AIC3107
    TLV320AIC3007
    TLV320AIC32

    Regarding the microphone preamplifier, you may take a look at these devices.

    http://www.ti.com/lit/ds/symlink/lmv1031.pdf
    http://www.ti.com/lit/ds/symlink/pga2505.pdf

    Please let me know if you have questions or comments on this. We will be glad to help you.

    Best regards,
    Luis Fernando Rodríguez S.

  • 0 in reply to Luis Fernando Rodriguez S.
    Intellectual 360 points

    Hi Luis,

    I was looking into the LM49250 and it seems it can do what I need.

    Table 4. Stereo Input Modes

    Input Mode L1_INSEL L2_INSEL Input Description
    0 0 0 Fully Differential Input Mode
    1 0 1 Single-ended input. R2 and L2
    selected
    2 1 0 Single-ended input. R1 and L1
    selected
    3 1 1

    Single-ended input. R1 mixed
    with R2 and L1 mixed with L2

    As see in the above table

    Mode 3 would mix the right and left inputs together before giving it into the output stage. So if I have 2 single ended stereo inputs can I connect like so,

    Stereo in 1 _L to L1
    Stereo in 1 _R to R1
    Stereo in 2 _L to L2
    Stereo in 2 _R to R2

    so in the above config if I understand correctly L1 and L2 with be pre-mixed and R1 and R2 will be pre-mixed and given to the Left and Right Headphone channels respectively.

    Also I see in the output mix table as follows

    Table 6. Headphone Multiplexer Control (continued)

    HPR_SSEL/
    HPL_SSEL    		 HPR_MSEL/
    HPL_MSEL    		 HPMODE HP_XSEL LEFT CHANNEL OUTPUT RIGHT CHANNEL OUTPUT
    3 0 1 1 M + L' M + R'
    4 1 0 0 R' L'
    5 1 0 1 M + R' M + L'
    6 1 1 0 L' + R' L' + R'
    7 1 1 1 M + L' + R' M + L' + R

    as can be seen Mode 3 allows to mix the mic channel with the L and R channels.

    The parts that you indicated seem to be quite powerful and feature rich however, I do not need advance features for this application, eg. I wouldn't be using I2S or the internal ADC/ DAC etc.

    What do you think about the LM49250?

  • 0 in reply to Alwyn DSouza
    TI__Guru* 84915 points

    Hi, Alwyn,

    Thank you for your details on this. 

    I agree with you. It will definitely cover your requirements based on the table that you attached. Its internal mixer allows to mix the line and microphone inputs to the same channel.

    Best regards,
    Luis Fernando Rodríguez S.

  • 0 in reply to Luis Fernando Rodriguez S.
    Intellectual 360 points

    Hi Luis,

    Thanks for the confirmation.

    Further to this I'm unable to find what are max levels the analog inputs of Line in and Mono in can accept.

    I looked into the electrical characteristics section but there is no such detail.

    Regards,

  • 0 in reply to Alwyn DSouza
    TI__Guru* 84915 points

    Hi, Alwyn,

    The maximum level for all the analog inputs is VDD.

    Exposing these inputs to a value outside -0.3V to VDD + 0.3V may result in a performance degradation and also in a circuit damage.

    Please let me know if you have additional questions or comments on this.

    Best regards,
    Luis Fernando Rodríguez S.