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Original question:

LME49720: popcorn noise

LME49720: Pop-cone noise

Mochi
Genius 4035 points
Part Number: LME49720
Other Parts Discussed in Thread: LM4562

Hello OP-amp team,

We got 4pcs of customer return of LME49720 caused by pop-cone noise issue.

I mounted those devices on the test circuit which has 40dB gain (1kR and 100kR) at +/-12V power supply with shorted differential input node.

Pop-cone noise level at particular channel is about 5mVpp 10msec duration, it is not acceptable level on our customers audio equipment even this behavior is come from common bipolar transistor.

Our customer wants to know TI's pop-cone noise level specification of this low noise audio purpose OP-amp.

Regards,

Mochizuki

  • 0
    Guru 36540 points

    Hi Mochizuki-san,

    As you know, the popcorn noise isn't specified in LME49720 data sheet, so please refer to the following links.

    LME49720: popcorn noise
    https://e2e.ti.com/support/audio/f/6/t/725471

    LM4562 / LME49720 low frequency noise
    https://e2e.ti.com/support/audio/f/6/t/415907

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    TI__Guru* 84915 points
    Mochizuki-san,

    Unfortunately, as Kato-san mentioned, this parameter is not specified in the datasheet since it may vary from application to application. We recommend to measure it in a test circuit or in the prototype circuit to get it.

    Best regards,
    Luis Fernando Rodríguez S.
  • 0 in reply to Luis Fernando Rodriguez S.
    Genius 4035 points

    Hello Kato-san,

    Thank you for your prompt advice, I over looked those useful related sleds.

     

    Hi Luis-san,

    As Andy mentioned in previous sled,

    >>It happens in wafer processing and it is very difficult to screen the devices with pop-corn noise within spec in testing process.

    So, this time we captured 10msec duration pop-cone noise, 1sec range duration step noise is difficult to testing but this type of "short period step noise" might be inside of testing spec. Is it correct?

    The other hand it says depended on bipolar wafer processing, do you see any variation on recent lot?

     

    Regards,

    Mochizuki

     

  • 0 in reply to Mochi
    TI__Guru* 84915 points
    Mochizuki-san,

    We haven't received information about variation on the recent wafer lots.

    Could you tell us if you get the same results on different boards and with different LME49720 units? Additionally, have you tried to reduce this noise with external capacitors? Could you try with 10pF capacitors and 0.1uF capacitors connected to GND? Could you also try with ferrite beads, please?

    Best regards,
    Luis Fernando Rodríguez S.
  • 0 in reply to Luis Fernando Rodriguez S.
    Genius 4035 points

    Hi Luis-san,

     

    Here is measurement data of 4pcs of customer returned devices at 40dB test circuit with +/-12V lab power supply.

    As we can see pop-cone noise is not channel depended, it is not power supply noise related step noise.

    Should we return those materials to you to confirm noise level on your final tester?

     

    Regards,

    Mochizuki

    LME49720 popcone.pdf

  • 0 in reply to Mochi
    TI__Guru* 84915 points
    Mochizuki-san,

    Is it confirmed that if all the 4 pcs are replaced for new ones, the pop-cone noise disappear?

    If so, you may proceed with the failure analysis request.

    Best regards,
    Luis Fernando Rodríguez S.
  • 0 in reply to Luis Fernando Rodriguez S.
    Genius 4035 points
    Luis-san,

    Thank you for your offering. Those devices are outlier of our customers end equipment noise specification, they replaced 4pcs of OP-amps at the factory then return it to us.
    I will proceed it to TI FA process.

    Regards,
    Mochizuki