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• TI Thinks Resolved

# LM4950: Some questions

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)

• 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.

• In reply to Luis Fernando Rodriguez S.:

Hi Sirs,

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

Input spec as follows

• In reply to Shu-Cheng LIN:

Hi Sirs,

Sorry to bother you.

Have any update on here?

Thanks!!

• In reply to Shu-Cheng LIN:

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.