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LM258: Is there any influence about output of LM258?

Lian Wu
Genius 5250 points
Part Number: LM258

Dears:

Could you kindly help to check the schematic and give some advice about it?

Is there any influence about DAOUT2 of LM258 if  power support is about 12.3V  and not 12V?

Thanks a lot!

Best regards

Luck Wu

  • 0
    TI__Mastermind 25775 points

    Hello Luck,

    Please understand that due to the US holiday, we have multiple team members out of the office on vacation. Most will be back next week, so please understand that there will be some delay if you have further questions.

    My initial impression is that the circuit looks reasonable. It is a straightforward non-inverting amplifier. I would make sure that the output voltage from the DAC is within the linear operating region of the LM258. For more information about input/output limitations, please see TI Precision Labs:


    www.ti.com/.../precision-labs.html


    Concerning 12.3V supply vs. 12.0V supply, there is very little difference. 12.3V is still within the operating region of the device.

  • 0 in reply to Pete%20Semig
    TI__Genius 15410 points

    Hello Luck,

    The LM258 has a specified operating supply voltage range of 3V to 30V. As Pete mentioned, as long as the device is operated within the specification of the device (common mode voltage, output swing limits, etc.) I do not see any issues using a 12.3V supply voltage.

    Is there a specific specification you are concerned about violating with a 12.3V supply?

    Thank you,

    Tim Claycomb

  • 0 in reply to Tim Claycomb
    Prodigy 50 points

    Hi Tim

          Thanks a lot for your reply,the output voltage of  LM258 is no more than 10V(the maximum value is 10V) ,the supply voltage of LM258 is 12V,if the supply voltage is larger than 12V(such as 13V),

    Whether or not the the output voltage of  LM258  is affected?

          And when the system start-up the output voltage of  LM258  will be 10V,when the Start completed the output voltage disappear,So considering the cpu is starting,the input of the LM258 is not controled .

    I used a dropdown resistance(1M)at pin3 and pin5,can solve the problem,But I don't whether or not the value of the dropdown resistance will affect the output voltage of  LM258?

         Thank you!

  • 0 in reply to gaogao01
    TI__Genius 15410 points

    Hello,

    The only effect changing the power supply from 10V to 12V will have on the amplifier is that the amplifier will be able to output a larger voltage. Please see output swing limitations (VOL and VOH) of the device.

    The LM258 can withstand up to 32V applied to the inputs while the supplies are at 0V. Please see section 8.3.3 in the LM258 datasheet. Therefore as long as the inputs do not go above 32V while the supplies are off (0V) the device will not be damaged.

    Thank you,

    Tim Claycomb

  • 0 in reply to gaogao01
    TI__Guru*** 139956 points
    Gao,

    The 1M ohm resistor will not affect the DAC voltage when it is set to active.
    When the DAC is high impedance at startup with no 1M resistor, the input bias current of the LM258 (-20nA) will pull up pin 3 (to about 10.5V) so the output will also rise to maximum high level (VOH). When the 1M is added, the input voltage will be about 20uA * 1Mohm = 20mV; the output will be about 60mV (problem solved).
  • 0 in reply to Ron Michallick
    Prodigy 50 points

    Hi Tim& Ronald,

    Thanks a lot for your reply,Could you kindly help to check the issue as below :

    If I reduce the value of the dropdown resistance(such as50K~1M)at pin3 and pin5 of LM258,Whether or not the the output voltage of  LM258  is affected?

     

    Thanks and Best Regards!

    Gao

  • 0 in reply to gaogao01
    TI__Genius 15410 points

    Hello Gao,

    Reducing the dropdown resistance will reduce the voltage at the input which reduces the voltage at the output. The voltage at the input is equal to Ib*R where Ib is the input bias current of the device and R is the dropdown resistance. The voltage at the output is equal to Ib*R*Gain.

    Thank you,

    Tim Claycomb