LM4990: Please help us with the review of the LM4990LD/NOPB audio amplifier design.

Hi, Sujitha,

Could you provide your circuit schematic, please? This would give us a better approach to this issue.

Thank you.

Best regards,
Luis Fernando Rodríguez S.

Hi, Sujitha,

Thank you for sharing the schematic circuit. In order to improve the signal quality, I would recommend few things:

- Ensure that VDD is completely stable, adding 0.1uF and 10uF capacitors will ensure that the ripple is reduced. Since this kind of devices is directly related to the VDD activity, the high ripple content may affect the output signal.

- Connect the thermal pad to GND, it is not internally connected.

- If an audio converter is being connected to the amplifier input, I would suggest to use an out-of-band filter ( https://www.ti.com/lit/an/slaa313a/slaa313a.pdf ). Otherwise, there's risk to amplify out-of-band content.

I hope this works for you. Please let me know if you have additional questions or comments.

Best regards,
Luis Fernando Rodríguez S.

where do i suppose to install 0.1uf and 10uf capacitors.

could you please give us more clarification of out of band filter in this scenario