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LM339-N: Input voltage range

masahiko shimizu
Guru 11235 points
Part Number: LM339-N
Other Parts Discussed in Thread: LM339, TLV3704

Hi,

My customer is using LM339-N.
He has questions about input voltage range.

Condition is V+ = 5V and V- = GND.
Q1: Can we use LM339-N with INPUT+ = +1V~+9V(swing signal) and INPUT- = +3.5Vdc(fixed value (REF)) at this condition?
Q2: Can we use LM339-N with INPUT- = +3.6Vdc(fixed value (REF)) at this condition?

Best regards,
Shimizu

  • 0
    TI__Mastermind 49926 points

    Hello Shimizu,

    The "Legal" input range is GND to VCC-2V (over temp). On a 5V supply, the legal input range is 0 to 3V.

    3.5V and 3.6V are above the legal input range.

    So, no, the input range is too high, and may result in incorrect output states. It may seem to "work" under the current conditions on the bench, but operation may be erratic over temp and device-to-device variation.

    What is the minimum response time you can tolerate? The TLV3704 family allows the input to go up to 5V above V+ (20V max), and would meet your requirements. However, it is a micropower comparator so it is much slower than the LM339. The quad pinouts are also different.

    Is it possible to divide down the input voltage? Comparators do not need an absolute value voltage, as long as both inputs are divided down equally.

  • 0 in reply to Paul Grohe
    Guru 11235 points
    Hi Paul-san,

    Thank you for your reply.
    I understand that commom mode voltage is "Vcc-2V(max)" at over tmp by your answer.

    Condition is V+ = 5V and V- = GND.
    Can we use LM339-N with INPUT+ = +1V~+9V(swing signal) and INPUT- = +3Vdc(fixed value (REF))?

    I cannot understand the mean of commom mode voltage range in datasheet.
    In comparators, I think that one of the input pins should be used within commom mode voltage range.
    Of cause, the else pin of the input pins must be used within absolute maxmum voltage range.
    Is it correct?

    Best regards,
    Shimizu
  • 0 in reply to masahiko shimizu
    TI__Mastermind 49926 points

    Hello Shimizu,

    For the LM339 family, yes, the output condition should be correct if *one* input is within common mode range.This is mentioned in table notes and the Apps section.

    THIS IS NOT TRUE FOR ALL COMAPRATORS!

    This is typical behavior of the LM339 family and is not warranted. Operating outside the specified ranges is always with risk with any device.

    Under the given conditions, the VREF is *at* the common mode limit with no margin. This is why I recommended the other part, or, decreasing the input levels (or even increasing the supply voltage).