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SN74LVC3G17: Input overshoot and undershoot actual value

Hung Ching Hsu
Expert 3086 points
Part Number: SN74LVC3G17

Dear,

I know the max input overshoot & undershoot value will be the absolute max/min rating of Vcc in the datasheet, and TI don't guarantee any operation outside this range.

But my customer would like to know the actual value of input overshoot & undershoot of SN74LVC3G17 and if it is possible to operate in the conditions as shown in the pictures.

I've learned from another e2e article, that logic which without clamp diode, the input overshoot under 1.3Vcc(=8.45V[6.5*1.3]) is acceptable(Actual Value).

And also the input undershoot under Vpeak-1(=-1.5V[-0.5-1]) within 10ns is acceptable(Actual Value).

According to above, I think overshoot (pic1, Vmax=6.8V) will be no problem.

But the undershoot(pic2, Vmin=-840mV, lasts 200ns) may cause the problem(because the period is too long). 

And what can be concerned if the overshoot & undershoot occurs 1000 times/sec?

Please let me know if I got anything wrong. 

  • 0
    TI__Mastermind 44985 points

    Hi Hung,

    First I would like to address the e2e posts you are referencing, can you link the actual thread for me? I think there may be some confusion caused by it.

  • 0 in reply to Dylan Hubbard
    TI__Expert 3086 points

    Hi Dylan

    Here's the link for your reference. It was written in Japanese.

    I also attach the English translation which is translated by google translation with some correction.

    Though I know there's no guarantee when the overshoot/undershoot is out of spec, the customer would like to know what might happen to the IC under the conditions I mentioned at the beginning.

    About the input overshoot

    http://e2e.ti.com/support/archive/jp/f/892/t/486703?HQS=dis-othe-null-faq_log-e2e-lp-ted-jp

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

    Although we cannot guarantee it, please understand the following as the ability value for reference.

For the overshoot tolerance of the input of the standard logic device,
There are differences depending on the presence or absence of a power clamp diode with a current path.

1. If the absolute maximum rating is VI: {VCC + 0.5V} MAX, the power clamp diode connected to the input exists.
In this case, the overshoot voltage is

Assuming that the clamp diode is not conducting
Up to about VCC + 1.0V within 10ns is considered as having no problem in practice.

As device series, HC / HCT, AC, CD4000B etc. belong to this.
    2. If the absolute maximum rating VI is simply specified by a numerical value, the power clamp diode
does not exist. In this case, the overshoot voltage can be considered simply by the withstand voltage.
VI of the absolute maximum rating Up to about 1.3 times the MAX value (1.1 times the VI for the ALVC series) is considered to be practically acceptable.

Device series include LV-A, LVT, LVC, ALVT, AVC, AUC, AUP, AHC / AHCT, ALVC
Etc. belong to this.」


    About the input undershoot

    https://e2e.ti.com/support/archive/jp/f/892/t/377666?HQS=dis-othe-null-faq_log-e2e-lp-ted-jp

    「Applying undershoot exceeding the lower limit of the input voltage specified in the absolute maximum rating of the data sheet is not guaranteed.

    However, as a guide outside the warranty, it is assumed that the protection diode is not turned on.
The undershoot which is Peak voltage to -1.0V within 10ns will not be a problem in actual use.
If you deviate from the absolute maximum rating lower limit, please understand that it is not covered by the warranty and make a judgment with reference to this guideline.」
  • 0 in reply to Hung Ching Hsu
    TI__Guru* 96947 points

    Hi Hung,

    That E2E post wasn't written by anyone on my team in Standard Logic. I can't speak to its accuracy, and I would recommend against using it as a reference for designs.

    To answer your questions:

    But my customer would like to know the actual value of input overshoot & undershoot of SN74LVC3G17 and if it is possible to operate in the conditions as shown in the pictures.


    "Actual value" I assume refers to the amount of overshoot/undershoot that you would expect to see in normal operation.  Unfortunately, overshoot and undershoot and extremely application dependent. If you are driving a very inductive load, your ringing will be excessive. If you are driving a very capacitive load, you will have very little ringing. Other factors also come into play, such as trace length and changes in transmission line impedance.

    If what you want to know is "How much can my signal exceed the absolute maximum ratings listed by," then the answer is much easier.

    For the positive side, applying a voltage above 5.5V (Recommended maximum voltage) can reduce reliability. Typically "reduced" reliability is still going to result in an extremely reliable device, considering the ratings of our devices. Exceeding 6.5V can cause immediate and catastrophic damage to the device. 

    For the negative side it's a little more complicated. Applying a voltage below 0V (Recommended minimum voltage) can reduce reliability. Exceeding -0.5V AND allowing more than 50mA to flow through the clamp diode can result in catastrophic damage to the device.

    It appears that the negative clamp diode is active for an extended period of time in this application - I would recommend measuring the current to determine if it exceeds 50mA, and if it does, add a limiting resistor to the input to prevent damage to the input.