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LM318-N: request schematic review

Genius 4800 points

Replies: 12

Views: 5109

Part Number: LM318-N

Hi,

The schematic below is circuit for a measurement control application, one of my main customers.

It seems blurry because resolution is not good, but please ask for a review.

thanks,

TS

  • TS,

    Is VLCO a negative voltage supply? What voltage?
    Is the first amplifier being used as a comparator?
    The capacitive load on second amplifier might be unstable.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    TS,

    LM318 is an unusual choice for a new design that doesn't leverage the 3 internal pins for performance tweaking. So I wonder if there may be a better new device.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    VLCD is negative voltage. -24V.
    And LM318 is used just a buffer, not comparator.
    If TI have another better device for this application, please let me know.
    thanks,
    TS
  • In reply to TS Yang:

    TS,

    I would need to know the input signal to know what op amp would work well.

    The marked out capacitor is bad for stability.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Hi Ron,

    thnaks for your help.

    Below is more detail infomations.

    U12, U11 component margin review

    - Proceed with component margin review through waveform measurement in normal circuit.

    1) Waveform measurement and margin check for U12 part

    (RMS, MAX, P-P, MIN is measured value.)

    PIN REF DATASHEET(MAXIMUM) RMS MAX P-P MIN MARGIN VOLTAGE(calculation) Remark
    2 IN- ±15V or midium value of VCC  1.22 3.2 5.3~-24.7 in spec
    3 IN+ ±15V or midium value of VCC 0.833 3.7 5.3~-24.7 in spec
    4 VCC- -20V -24.4V -29.7 in spec
    6 OUT -21.57 5.2 27.9 -22.7 -
    7 VCC+ 20V 5 12.3 in spec

    * Input range calculation

    1) midium value of VCC : -9.7V((-24.4+5)/2)

    2) Maximum range of VCC

    - VCC+ : -9.7 + 20 = 12.3V

    - VCC- : -9.7 - 20 = -29.7V

    3) Maximum range of VIN

    - VIN+ : -9.7 + 15 = 5.3V

    - VIN- : -9.7 - 15 = -24.7V

    Oscilloscpe capture for each pin of U12

    U12 wave.pdf

    2) Waveform measurement and margin check for U11 part

    (RMS, MAX, P-P, MIN is measured value.)

    PIN REF DATASHEET(MAXIMUM) RMS MAX P-P MIN MARGIN VOLTAGE(calculation) Remark
    2 IN- ±15V or midium value of VCC  -20.15 5.3~-24.7 in spec
    3 IN+ ±15V or midium value of VCC -20.18 5.3~-24.7 in spec
    4 VCC- -20V -24.4V -29.7 in spec
    6 OUT -20.15 -
    7 VCC+ 20V 5 12.3 in spec

    * Input range calculation

    1) midium value of VCC : -9.7V((-24.4+5)/2)

    2) Maximum range of VCC

    - VCC+ : -9.7 + 20 = 12.3V

    - VCC- : -9.7 - 20 = -29.7V

    3) Maximum range of VIN

    - VIN+ : -9.7 + 15 = 5.3V

    - VIN- : -9.7 - 15 = -24.7V

    Oscilloscpe capture for each pin of U12

    U11 wave.pdf

    thanks,

    TS

  • In reply to TS Yang:

    TS,

    It looks like the circuit is working well. Do you have any concern about the results?

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Hi Ron,

    thanks for your answer.

    I have one more simple question regarding the cap you mentioned above.
    On DATASHEET, there is no value for output CAP. How much should I choose?
    Is there any maximum value that TI recommends?

    And if there's any reference schematic for LM318, please share for us.

    thanks,
    TS
  • In reply to TS Yang:

    TS,

    The best capacitance is no capacitance. This is true of almost all op amps.
    If a low pass filter is needed after the op-amp output then use a resistor capacitor filter.

    There is no reference schematic.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    HI Ronald,

    Perhaps this is my last question regarding this issue,

    As you mentioned in the previous answer, you said that "The best capacitance is no capacitance. This is true of almost all op amps."

    Can you explain this in more detail?

    If you have any material or documents related to this, please share it.

    Any advice is welcome.

    thanks,

    TS

  • In reply to TS Yang:

    TS,

    I suggest the stability section of the precision labs vides for op amps.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

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