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LM4562 / LME49720 low frequency noise

Prodigy 225 points

Replies: 29

Views: 17740

I was ordered about 400pcs of these chips in SO8 package from Farnell and from Digikey within some years period. I am using these chips for ultra low distortion audio range sine oscillators manufacturing. But, I need to make noise spectrum measurement control before trying these chips, because situation is non understanding for me in frequency region lower than 100Hz. Only approximately half of all chips has noise density in this region similar as in higher frequency region, but approximately 20% of all chips has very high noise and flicker (more than ten times higher) in this low frequency region. In other ways these chips are very nice, and allow to build oscillators with distortions level about -150dB at 1kHz.

Thank  you,

Victor.

 

29 Replies

  • Hi CC,
     
    Sosun 会统一把上次培训的文件发出来。谢谢!

    Thank you and Best Regards!
    Roman Wang/王良藩
    Signal Chain Analog FAE,DongGuan
    Mobile: 139-1665-8076
     
     
     
  • Hi Victor,

    Which kind of help do you need from us?

    Andy
  • In reply to Andy Liu (BMS):

    Hi, Andy.

    Please advise, if you can, that observed situation is normal, or maybe something is wrong.

    Thank you.

  • In reply to Victor Mickevich:

    Hi Victor,

    Here is what I know about these two parts:
    Noise test is implemented for these two parts but measurement time is pretty short. In the noise test, it is very hard to screen 100% noisy parts.

    Andy
  • In reply to Andy Liu (BMS):

    Hi,

    Here are some pictures of spectrum measured in same conditions.

    1) very good chips (around 50% of all quantity):

    2) good chips (around 30% of all quantity):

    3) Noisy chips (around 10% of all quantity). Two pictures from different chips)

    4) Very noisy chips (around 10% of all quantity). Three pictures from different chips:

    Last chip measured in wider frequency range:

  • In reply to Victor Mickevich:

    Hi Victor,

    Thanks for these pictures you posted.

    The wafer process of LM4562/LME49720 is Bip process and sometimes the Bip process causes the pop-corn noise or burst noise problem. Any Bip process op-amp has the possibility of pop-corn or burst noise sometimes. It happens in wafer processing and it is very difficult to screen the devices with pop-corn noise within spec in testing process.

    Andy
  • In reply to Andy Liu (BMS):

    Hi,
    Thank you Andy for the advice. If I properly understand, then it is no way for to use these chips without user's input control, when excellent performance is needed in all audio range.
  • In reply to Victor Mickevich:

    Hi Victor,

    In my opinion, if you really care about the "excellent performance in all audio range", I suggest you do the screening by yourself. Sorry, it is not a very good answer, but I cannot offer you a better one. 

    Andy

  • I am also seeing burst noise in various production lots of the DIP LME49720 and LME49860. This was observed at the output of a 40 dB gain instrumentation amp input. The NJM5532, NJM2114, NJM2068 and MC33078 do not exhibit this burst noise in the same circuit and same PC board.


    It sometimes takes several seconds to occur so if the test time is short, parts with this defect are not screened. This LME49720 sample was a brand-new from the tube lot JR18ABE3.


  • In reply to Wayne Kirkwood:

    Hi, Wayne, Victor,

    As Andy mentioned, it might be difficult for us to 100% fully screen out all these parts.

    However, if you would like to return these to where you purchased them, they can send them back to use for Device Analysis so perhaps we can improve the test program to better try and screen this effect out for you.

    We are always looking to continually improve.

    -d2

    Best regards,

    Don Dapkus

    Gate Driver Applications

    Dallas, TX USA

     

    We have an excellent training series that can help answer all your questions about our gate drivers. It is indexed so you can jump right to the section you want! You can find it here. A second series focused 100% on Isolated Gate drivers may be found here.

    We also provide models for our gate drivers to accelerate your time to market. You can find them in the Product Folders under the "Design and development" tab:

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