• State Resolved
  • Locked Locked
  • Replies 8 replies
  • Answers 3 answers
  • Subscribers 28 subscribers
  • Views 413 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

LM386: Could you please tell me how to remove pop noise at powered up?

LM386: Is it O.K. to connect 0.1uF and 3.3ohm or 4.7ohm between VOUT(No.5) and GND to avoid output osccilation?

Kazuya Nakai59
Guru 20100 points
Part Number: LM386
Other Parts Discussed in Thread: LM384

 Hello guys,

 One of my customers is evaluationg LM386 for their new products.

 In the evaluation, they faced LM386 output osccilation and pop-noise generation.

 They have the follwong questions. Could you please give me your reply?

Q1. They confirmed the following things to eliminate the osccilation.

  1. De-coupling capacitor between Vs(No.6) and GND(No.4) is placed near by LM386.

  2. Ripple voltage of Vs(No.6)-GND(No.4) os less than 20mV.

  3. The output osccilation couldn't eliminated though 1uF/10uF seramic capacitor is attached

      between BYPASS(No.7)- GND(No.4).

       But they could eliminate the osccilation when 0.1uF and 4.7ohm or 3.3ohm was attached

      between VOUT(No.5)  - GND.

       Their question is "Is ther any problem to attach this resistor and capasitor between VOUT-GND?".

Q2. They found pop noise is generated when LM386 is powered up

      even if -input (No.2) and +input(No.3) are connected to GND.

      Their question is "Could you please tell me pop-noise generation mechanizm.

      Does TI have any document about pop noise?".

 Your reply would be much appreciated.

 Best regards,

 Kazuya.

  

  • 0
    TI__Guru* 95165 points

    Hi Kazuya-san,

    Q1: those components (resistor and capacitor to GND) are actually recommended from the data sheet. Figure 10 and some other diagrams show these components that help to prevent oscillations. So there is no problem with this solution.

    Q2: pop noise is usually caused by mismatch between the inputs, or it can also be due to capacitor charge/discharge in the signal path. There are a couple pop related documents that could help understand it, although they're not focused on LM386:

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

  • 0 in reply to Ivan Salazar
    Guru 20100 points

     Hello Ivan,

     Thank you very much for your reply.

     Could I ask you a few additional questions as the following?

    1. Could you tell me how to calculate the R and C placed between OUTPUT and GND?

    2. Is any pop noise not generated from LM384 at LM384 power up when "-IN" pin and "+IN" pin are connected to GND?

    3. Is it effective for eliminate osccilation to separate No.7 GND pin from No.3,4,5,10,11,12 pin with PCB pattern layout?

    4. The customer think the osccilation level would be changed due to temperature and product(LM384) valiation.

        How much margin of C and R should be taken for the temp and product variation?

     Thank you and best regards,

     Kazuya.

     

     

  • 0 in reply to Kazuya Nakai59
    TI__Guru* 95165 points

    Kazuya-san,

    You should use the RC values from the data sheet, this applies for both LM386 and LM384. You can try th

    Isolating pin 3, 4, 5, 10, 11 and 12 could help to reduce the noise, although it is not related to oscillation.

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

  • 0 in reply to Ivan Salazar
    Guru 20100 points

     Hello Ivan,

     I understood 0.05uF + 10ohm are recommended for eliminating the output oscillation.

     But the customer case, the oscillation could not be eliminated with 0.05uF + 10ohm.

     They could eliminate the oscillation with 0.1uF and 4.7ohm or 3.3ohm.

     They have a few questions as the follows.

     Q1. Is there any possiblity that these RC (0.1uF and 4.7ohm or 3.3ohm) damage LM386?

     Q2. The customer thinks the oscillation level would be changed due to temperature and products(LM384/LM386) valiation.

        How much margin of C and R should be taken for the temp and product variation?

        Is this difficult to answer? Should the customer test it at high/low temperature?

     Thank you and best regards,

     Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Guru* 95165 points

    Kazuya-san,

    Q1: I wouldn't expect the proposed RC values to damage LM386, it should be safe to use these component values.

    Q2: Due to the age of the device and reduced information about it, it's a bit hard to provide such details. If possible I would suggest to test on high/low temp as you mention for reliability purposes.

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

  • 0 in reply to Ivan Salazar
    Guru 20100 points

     Hello Ivan,

     Thank you very much for your reply and I'm sorry to be late response.

     Could I ask you an additional question because the customer asked as the below?

    Q.  What is the reason that your said " I wouldn't expect the proposed RC values to damage LM386, it should be safe to use these component values."?

          Is the reason that the output current is enough to drive those components?

     Thank you very much again and best regards,

     Kazuya. 

  • 0 in reply to Kazuya Nakai59
    TI__Guru* 95165 points

    Hi Kazuya-san,

    That is correct, LM386 should be OK to operate with the proposed component values.

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

  • 0 in reply to Ivan Salazar
    Guru 20100 points

     Hi Ivan,

     Thank you very much for your supports

     Best regards,

     Kazuya.