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About unused channel of LM358 and LM339

Satoshi
Guru 19685 points

Other Parts Discussed in Thread: LM339, LM358, LM393-N, LM393

Customer will connect unused channel of LM358 and LM339 (please see below), is this correct?

※VIN+：+15V, VIN-：GND

Customer is already made these circuit, they doesn't want to change as much as possible.

Best regards,

Satoshi

  • 0
    TI__Guru**** 172306 points
    Satoshi san,

    There is no harm provided the ground pin (VCC-) is also grounded.

    If ground of device goes to negative supply, then I prefer input resistor on grounded pin.
  • 0
    TI__Guru 67706 points

    Hi Satoshi,

    For the LM358, the output should be connected to the inverting (-)  input. As shown, it may oscillate due to positive feedback if the offset crosses zero.

    The LM393 is an open collector output comparator, so essentially the non-inverting input is (mostly) floating as shown. As stated in the (LM393-N) datasheet apps section, all unused inputs can be tied to GND. Leave the unused outputs floating with no pullup resistor.

    Regards,

  • 0 in reply to Paul Grohe
    Guru 19685 points
    Ronald-san, Paul-san

    Thank you for reply.
    Sorry for additional question, please let me know;

    When customer circuit is oparate (I posted and attached mistake circuit), what ploblem occur?
    I specially want to know possibility of damage.
    (Or, is it only oscillate?)

    Best regards,
    Satoshi
  • 0 in reply to Satoshi
    TI__Guru**** 172306 points
    Satoshi san,

    For LM393, inverting is ground so ouput will go high or more accurately open (off). The non-inverting input (and output) will be a little above zero.

    For LM358, the output will probably go high (VCC -1.4V) and stay there. If the output was low due to a negative VIO then the output would stay low but might go high if disturbed.

    I do not expect any damage or undesirable effects on the used channels.

    Paul may have a different view.
  • 0 in reply to Ron Michallick
    Guru 19685 points
    Paul-san

    If you have information of "possibility of damage", please let me know.

    Best regards,
    Satoshi
  • 0 in reply to Satoshi
    Guru 19685 points
    Paul-san

    Any update on this?
    I think that difficult contents, please help me if there is any information.

    Best regards,
    Satoshi