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SN74AC14: Please tell me about the case where the undershoot is below -0.5V.

user4691663
Prodigy 40 points
Part Number: SN74AC14

Hello.

Please tell me about the case where the undershoot is below -0.5V.
Not found on the datasheet.

If the input waveform is -0.5V or less, are there any relaxation conditions according to the time regulation?

For example
If the input voltage below -0.5V is 20ns or less, up to -1.0V is acceptable.
Such

Regurd,

 Hirofumi Yamaguchi

  • 0
    TI__Guru* 96591 points

    Hello Yamaguchi-san,

    The datasheet is clear on this:

    You may exceed -0.5V so long as the current does not exceed the rated maximum. There is no time limitation.

  • 0 in reply to Emrys Maier
    Prodigy 40 points

    Hello Emrys Maier,

    thank you for your answer. I have an additional question below.
    We are currently measuring the waveform with an oscilloscope.

    (1) Undershoot of input pin
    　If the input current is 20mA or less, the undershoot will be -1.0V. Will this lead to component failure?

    (2) Allowable voltage value for undershoot of input pin
    　What V can undershoot be allowed when the input current is 20mA or less?

    Regards,

    　Yamaguchi

  • +1 in reply to user4691663
    TI__Guru* 96591 points

    Hello Yamaguchi-san,

    (1) If the input current is limited to 20 mA or less, you are operating within the datasheet specifications and I already said this is the recommendation of TI, so obviously no, it will not cause failure.

    (2) In order to meet the datasheet specification you must limit the current. There is no exception for this and there is no listed limitation for voltage. I cannot guarantee anything else.

    If this is a concern in your system, a series resistor can be used to ensure that input current does not exceed 20mA. The undershoot value listed of -1V would then require a series resistor of value 1 / .02 = 50 ohms. Personally, I would use a 100 ohm resistor because (a) that's a 5% resistor value that's commonly available and (b) it will keep the current far below the rated maximum. Generally it's a bad idea to operate a device near the limits (are you sure it's -1V and not -1.05V?).