LM4861: When a sound is played, a noise is detected at in the initial part of the sound.

Andy Kim54

Part Number: LM4861

Hello.

We develop a system, including the audio amp, LM4861.
There is a sound noise issue related with the LM4861.
The sound noise is detected in the following cases.

1. After the audio codec output signal is input to the LM4861, and then the LM4861's shutdown pin becomes Low(low active)
2. After the LM4861's shutdown pin is Low, and then the audio codec output signal is input to the LM4861.

I have mentioned in detail this issue in the attached file.

Thanks.

alc5621_amp circuit.pdf

over 7 years ago

0 Andy Kim54 over 7 years ago

Prodigy 40 points

Attache files : sound noise_20170914.pptx, alc5621_amp circuit.pdf

0 Ivan Salazar over 7 years ago

TI__Guru** 102065 points

Hi Andy,

Welcome to e2e.
I've asked one of my colleagues to take a look at your post.
He'll come back with more detail.

Best regards,
-Ivan Salazar
Audio Applications Engineer - Low Power Audio & Actuators

0 José Luis over 7 years ago in reply to Andy Kim54

TI__Mastermind 20085 points

Hi Andy,

This kind of noise is called Pop noise and it is produced when the device turns on very fast.
The bypass capacitor determines how fast the device turns on. You must reduce the Bypass capacitors in order to avoid Pop noise. The Bypass capacitor should be approximately of 1uF and should be placed as close as to the device.

Best Regards
José Luis Figueroa
Applications Engineer

0 Andy Kim54 over 7 years ago in reply to José Luis

Prodigy 40 points

Hi José Luis Figueroa,

Thanks for your reply.
I will check it.

Best Regards
Andy

0 Andy Kim54 over 7 years ago in reply to José Luis

Prodigy 40 points

sound noise_20170921.pptxDear José Luis Figueroa

We have tried some modification by referring to your recommendation like the attached document.
(Reduce TC2/TC3 to 1uF, TC1 to 1uF)

But we didn't find any improvement.

Could you let me know in detail which capacitor we should reduce or add or remove?

Best Regards
Andy

0 José Luis over 7 years ago in reply to Andy Kim54

TI__Mastermind 20085 points

Andy,

The bypass capacitor is TC3 and you just had to change this one. This capacitor is connected to the bypass pin.
Keep in mind that you must use ceramic capacitors made of temperature coefficients of X5R, X7R, or better and should be placed as close as possible to the device in order to get the best performance possible.

Best Regards
José Luis Figueroa
Audio Applications Engineer

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LM4861: When a sound is played, a noise is detected at in the initial part of the sound.