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LM386: Use pin 7 as mute?

user5018898
Intellectual 770 points
Part Number: LM386

Hi

My customer is noticing that in a design they have the LM386 has a noise (hissing) on the output when there is a steady input of +1.8V on pin 3. The customer came across a website stating that if he grounds pin 7 (BYPASS pin) instead of using a 10uF cap, this will mute the output and eliminate the noise. He is planning to add a mux to pin 7 either connect 10uF (in normal operation) or ground it in speaker off condition.

 

Another point the webpage he looked at made was that the inverting input is less noisy than the non-inverting input.

 

Can you confirm if this is ok to do and provide any other recommendations?

Thanks, 

Jose

  • 0
    TI__Guru* 84915 points

    Hi, Jose,

    We are not aware of this configuration to reduce hissing noise. If the customer would like to use this configuration for his application, we cannot guarantee it will work since our datasheet recommends a capacitor to GND.

    What we can recommend is to ensure that all the power supplies are fully stable and the decoupling capacitors are placed as close as possible to the power pins.

    Also, does the customer have additional components on the board sharing the same power and ground path? If he removes these components, is the hissing noise still present? I'm asking this in order to verify what the root cause could be.

    Thank you.

    Best regards,
    Luis Fernando Rodríguez S.

  • 0 in reply to Luis Fernando Rodriguez S.
    TI__Guru* 84915 points

    Hi, Jose,

    I'm closing this e2e thread due to the inactivity. However, feel free to post any additional question or comment about this case. We will be glad to help you.

    Best regards,
    Luis Fernando Rodríguez S.