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LM4950: Some questions

Shu-Cheng LIN
Guru 11785 points
Part Number: LM4950

Hi Sirs,

Sorry to bother you.

If we use LM4950, speaker is 4ohm/2w (Use SE)

Is it based on the following figure to determine the output voltage??

The AMP front-end input (AUDIO CODEC output) should be 1.2~1.1 Vrms

Will the setting of gain as shown below be correct ??(speaker is 4ohm / 2W)

  • 0
    TI__Guru* 84915 points

    Hi, Shu-Cheng,

    Please take a look at my responses below and let me know if you have additional questions or comments on it.

    If we use LM4950, speaker is 4ohm/2w (Use SE) Is it based on the following figure to determine the output voltage??

    Yes, figure 23 of datasheet shows the output power that you may reach for a RL = 4ohms (SE operation) with a THD+N = 10% and THD+N = 1%. You would need to select the power supply according to your power requirements.

    Will the setting of gain as shown below be correct ??(speaker is 4ohm / 2W)

    This resistors configuration results in a gain of ~16.3. Could you provide details about the input that you will be using and the expected output?

    Best regards,
    Luis Fernando Rodríguez S.

  • 0 in reply to Luis Fernando Rodriguez S.
    Guru 11785 points

    Hi Sirs,

    Thanks for your reply.

    Please help confirm the LM4950 schematic (Single-Ended)

    LM4950_0815-Edit.pdf
    The line below CN9 is anti-pops

    Input spec as follows

  • 0 in reply to Shu-Cheng LIN
    Guru 11785 points

    Hi Sirs,

    Sorry to bother you.

    Have any update on here?

    Thanks!!

  • 0 in reply to Shu-Cheng LIN
    TI__Guru* 84915 points

    Hi, Shu-Cheng,

    Sorry for the delay on this.

    I already reviewed the schematic and everything seems to be in order. I didn't find anything to modify.

    The configured gain in this case is given by Rf / RI = (48.7K / 20K) = 2.435. If a 1.2 Vrms signal is used, you should be able to reach almost 2.9Vrms at the output. This would be enough to reach 2W output power with a 4ohms load.

    Best regards,
    Luis Fernando Rodríguez S.