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SN74LV86A: About over shoot

soichiro kikuchi
Prodigy 140 points
Part Number: SN74LV86A

Overshoot 9.2V was applied to the input terminal.Do you know the current value at this time?

Even if I checked the current value, the parameter in the IBIS model was only up to 5V.

Can you show that there is no problem with the performance of the part?

waveform.pdf

  • 0
    Guru 279850 points

    The absolute maximum rating is 7 V. This voltage is forbidden and will degrade or even damage the device. (LV-A inputs have no clamping diode to VCC, so no current is allowed to flow.)

    Oscilloscope probes can introduce ringing. To avoid this, use a ground spring instead of a ground clip.

    To avoid ringing on the signal line, properly terminate the trace. The easiest way to do this is to add a source termination resistor (e.g., 33 Ω) at the driver.

  • 0 in reply to Clemens Ladisch
    Prodigy 140 points

    Hi Clemens.

    As you suggested,adding termination resistor is the easiest way. Unfortunately, this method does not meet the shipping time of the product.

    I have seen the attached thread.(Sorry in Japanese.)

    This method tolerates up to 9.1V. Since it is written that it is about 9.1V, is 9.2V not allowed?

    We do not ask for guarantees.

    thread.pdf

  • 0 in reply to soichiro kikuchi
    Guru 279850 points

    Please link to the thread.

  • 0 in reply to Clemens Ladisch
    Prodigy 140 points

    Sorry,It seems that this thread is not currently posted.

    Shall I send you an English translation?

  • 0 in reply to soichiro kikuchi
    Guru 279850 points

    Yes, please do.

  • 0 in reply to Clemens Ladisch
    Prodigy 140 points

    Sorry for the late reply.

    Title：To what extent is input overshoot allowed for standard logic?

    The warranty of the device is the absolute maximum rating value specified in the data sheet.

    It cannot be guaranteed, but the ability value is as follows for reference.

     

    The overshoot immunity of a standard logic device depends on the presence or absence of a power-clamp diode with a current path from the input terminal to Vcc.

    (In the case of SN74LV86A, the following )

     

    If the VI is rated at absolute maximum, but is simply specified numerically, there is no power clamp diode at the input.

     

    In this case, the overshoot voltage can simply be thought of in terms of isolation voltage.

     

    We believe that there is practically no problem up to about 1.3 times the absolute maximum rated VIMAX (1.1 times for the ALVC series).

  • +1 in reply to soichiro kikuchi
    TI__Mastermind 19450 points

    Hi Soichiro,

    Clemens is correct here. Simply put, the absolute maximum voltage on the datasheet is a hard stop.

    Anything exceeding that absolute maximum voltage, including oscillations and ringing, is liable to degrade or even immediately damage the device, especially because there is no positive input clamping diode on this device. Even by the guidelines of that thread, your device still exceeds the number they give (9.2V > 1.3 x 7 = 9.1V).

    Maybe the device will work despite seeing a consistent 9.2V overshoot: our devices are considerably robust. Even so, TI can't make any guarantees towards the performance or reliability of the device in that circumstance.

    You should definitely follow up on Clemens' advice and make sure that your oscilloscope probe isn't introducing any additional ringing. It's possible that the device is not actually seeing 9.2V overshoot, and that's just noise introduced by the probe.

    Best,

    Malcolm