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LM2903-Q1: About LM2903 unused pins

Noriaki Fukazawa
Expert 1620 points
Part Number: LM2903-Q1
Other Parts Discussed in Thread: LM2903, LM393-N, LM393,

Hi Expert,

I have a question about LM2903 unused pins.

My customers are using only one of the LM2903 2in1, unused part 6PIN = open, 7, 8PIN = GND short circuited.

Customers are concerned about the following points.

① Does the unused PIN processing method comply with the manufacturer's recommendation?
② If you are not using the recommended method recommended by the manufacturer, please present the recommendation.
③ What are the implications of the current unused PIN processing method? (Increase / decrease in current?

Best,Regars.

Noriaki

  • 0
    TI__Guru 60786 points
    Hello Noriaki,

    As specified in the sister LM393-N datasheet applications section, the unused inputs can be grounded (connected to Pin 4) and the unused output left floating.

    The LM2903-Q1 is fundamentally equivalent to the LM393, so the recommendation still applies.

    Per the internal design, the supply current changes a few percent according to the output level due to internal current paths changing. Grounding the inputs insures that the outputs do not randomly change due to floating inputs. But the output condition (high or low) is not guaranteed because of the effect of ±15mV offset causing the output to go high or low according to the particular device offset polarity. Because the output does not have a pull up resistor - the output does not really change.
  • 0 in reply to Paul Grohe
    Expert 1620 points
    Hello Pauel-san,

    Thank you for your answer.
    I understood how to process input / output pins.
    Is it okay with my customer that pin processing is correct?

    Best,Regars.
    Noriaki
  • 0 in reply to Noriaki Fukazawa
    Expert 1620 points
    Hello Paul-san,

    There is a point I would like you to ask about this product additionally.

    1.
    The description in "9.1 Application Information" can be seen as the entry of unused PIN.
    Is there a statement somewhere that "open output is recommended for unused output terminals"?

    2.
    The following sentences can be seen in "8.4 Device Functional Modes".
    "All pins of any unused comparators should be tied to the negative supply."
    Does this mean that output is also connected to GND?
    However, with this recommendation, Output and GND are short-circuited in my customers circuit.

    Thank you very much for your support .

    Best,Regars.
    Noriaki
  • 0 in reply to Noriaki Fukazawa
    TI__Guru 60786 points

    Hello Noriaki,

    There is no specific statement in either datasheet as what to do with the unused output.

    The output is an "open collector" output, which can only sink to GND. It cannot source current, so it cannot go "high" without the external pull-up resistor. Essentially, the output is a switch to ground. No current will flow by grounding a grounded switch...

    The output is designed to be "wire OR'ed" with other outputs, so the output is designed to be "grounded" externally by another device. So grounding the output is not a problem and is an acceptable solution.

    I just recommend leaving the output unconnected to eliminate a possible leakage current path (up to 1uA) and to allow the use of a rail-to-rail output device if the circuit is rev'ed or substituted in the future.

    So the LMx93/LM2903 unused output can be grounded or left open - it is up to the designer.