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SN74LVC2G125: impact of slow input edge rate on lifetime

Ryuji
Guru 20090 points
Part Number: SN74LVC2G125

Hello,

If SN74LV2G125 is used under the following conditions, will it affect the life span?
If given, how much can quantitative data be presented?

Vcc=2.5V
Δt/Δv I= 5usec/V
Frequency  10times/Day

Our customer understood that the output may oscillate on the slow input edge rate.
However they can not avoid this condition on their system. Therefore, they want to know whether device life will be affected and actual value.

Best Regards,
Ryuji

  • 0
    Guru 316780 points

    The FAQ says that this "can cause …  damage to the device."

    And there is a report of devices that actually have failed.

  • 0 in reply to Clemens Ladisch
    Guru 20090 points
    Hello Clemens san,

    Thank you for the reply.

    Could you please let me know the damage mechanism?

    I think that the damage mechanism is the following.

    If the input is in the threshold region, a through current flows through the device and Icc increases.
    As Icc increases, the device generates heat.
    It is destroyed when exceeding Tj of the device due to heat generation.
    In addition, flowing through current affects the life of the device.

    Is my understanding correct?

    Best Regards,
    Ryuji Asaka
  • 0 in reply to Ryuji
    Guru 316780 points

    Implications of Slow or Floating CMOS Inputs (SCBA004) says:

    If a voltage between 0.8 V and 2 V is applied to the input for a prolonged period of time, this situation becomes critical and should not be ignored, especially with higher bit count and more dense packages (SSOP, TSSOP). For example, if an 18-bit transceiver has 36 I/O pins floating at the threshold, the current from VCC can be as high as 150 mA to 200 mA. This is approximately 1 W of power consumed by the device, which leads to a serious overheating problem. This continuous overheating of the device affects its reliability. Also, because the inputs are in the threshold region, the outputs tend to oscillate, resulting in damage to the internal circuit over a long period of time.

  • 0 in reply to Clemens Ladisch
    Guru 20090 points
    Hello

    I checked this application note.
    SN74LVC2G125 is 2 bit device. Thus, I think that the Vcc is not so high.

    Even if the slow input edge rate , I think that there is no damage unless it violates the absolute maximum rated Tj, voltage.
    Is this understanding wrong?

    If damage is given by oscillation, what kind of cause is it?
    Is it that the absolute maximum rating of the output is exceeded by oscillation?

    Regards,
    Ryuji
  • 0 in reply to Ryuji
    Guru 316780 points
    I'd guess that the oscillations are faster than the switching that can happen due to external signals. Furthermore, not only the input transistors but all internal transistors of the device are kept in the transition region for a longer time.
  • 0 in reply to Ryuji
    Guru 316780 points
    MOSFETs have a negative temperature coefficient when the gate-to-source voltage is too small. So when the input voltage is in the invalid region for too long, you can get hot spots and thermal runaway in the input transistors.
  • 0 in reply to Clemens Ladisch
    Guru 20090 points
    Hello Clemens san,

    Thank you for the reply. I understood the cause of thermal.


    The device is not damaged if the device is used within the absolute maximum ratings(voltage, current , temperature).
    Is my understanding correct?

    I think that If the device may be damaged when Δt/Δv was violated even if using within the absolute maximum ratings, we should add the Δt/Δv to the absolute maximum ratings table.

    Best Regards,
    Ryuji
  • 0 in reply to Ryuji
    Guru 316780 points

    The absolute maximum ratings specify the limits beyond which the device might fail immediately.

    Footnote (1) of the Absolute Maximum Ratings table says:

    Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

    So if you go beyond the recommended operating conditions, the device can also fail, but more slowly.