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LME4972/ LM4562 Questions

Christopher Cuccia
Prodigy 150 points
Other Parts Discussed in Thread: LME49720, LM4562

Dear Engineers,

I have two questions regarding this operational amplifier.....

1) What is the common mode input capacitance for the amplifier. It is not listed on your datasheet I do not believe.

2) So I am interested in using this amplifier for its use as an RIAA Phono Stage. The typical application schematics you have for this use state that data is derived from a 10mV signal and brought up to roughly .5volts for a gain of 50. I am interested in feeding in a 5mV signal which is the normal voltage off of a moving magnet cartridge and then with that input, still coming out with a gain of .5V for a total gain of about 100. Is this problematic with this amp concerning signal to noise ratios or other common mode noise concerns? Will I be able to reap similar performance results and is this something that you forsee as working out okay or shall I boost the signal through an additional stage instead of one.

Sincerely,

Christopher Cuccia

  • 0
    TI__Guru** 110925 points
    Hi Christopher,

    I will try to find the information you requested.
    I will come back as soon as possible.

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0
    TI__Guru** 110925 points
    Christopher,

    Unfortunately there is no information available regarding LME49720/LM4562 input capacitance.
    Regarding the high gain application, this device should be able to work fine although higher gain usually causes noise increment. You could try it and evaluate its performance.

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0
    Genius 3295 points

    Hi Christopher,

    Regarding your questions:

    1.) Not sure why the common mode capacitance isn't listed. Other devices list this...odd.

    2.) (LM4562 datasheet) Figure 110 shows the RIAA preamp, plus an additional gain stage. You should have no issues whatsoever with "gaining up" the signal after the first stage (providing you're using a good low-noise dual power supply of +/-15V or so). I would be far more concerned with PCB layout, component selection, etc. than the opamp itself. Maybe even use a differential input stage if the wires between the cartridge head and preamp is far...

    Mike Tripoli 

  • 0 in reply to Ivan Salazar
    Prodigy 150 points

    Do you have a ballpark idea of what you believe the capacitance would be even if a conservative guesstimate. It's really important I have at least something to work on.

    Chris

  • 0 in reply to Christopher Cuccia
    Genius 3295 points
    Hi Chris,

    Tough challenge... one has to consider the package, the input structure of the device, etc. ad nauseam. If you have a good LCR meter, you could try measuring it yourself (though the test jig itself is going to be tough).

    You could build the circuit and then do AC sweeps and plot the results; at the end of the day, this is going to be the best solution, you can then adjust the input of the circuit exactly for the response you need. If it were me, this would be my approach as you're the one controlling all the parameters, regardless of published spec's.

    It's not a great suggestion; look at some other datasheets and extrapolate from there...

    Mike Tripoli