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SN74LVC2G86: Input threshold voltage level

Vincent Li00
Intellectual 2035 points
Part Number: SN74LVC2G86

Hi Guys

Customer is using our SN74LVC2G86. There is a detailed question about the input logic voltage level:

There are two understandings of Vih in the SN74LVC2G86 SPEC:

1. The minimum Vih value is 2V, assuming Vih is 2.1V, indicating that the input voltage is greater than 2V, the logic is H; when the input voltage is 2.0V, it is less than Voh, then the logic is L; If the input voltage is 1.9V, the judgment logic is L because it must be less than the Vih value;
2. If the input voltage is greater than or equal to 2V, it is judged as H; in order to meet the requirements of the actual chip, it is possible to judge the logic to be H at 1.9V or 1.95V or 1.98V;

So Which one is correct? Or what is the correct way to understand the Vih of the logic voltage?

Thank you~

Thanks

-Pengfei

  • 0
    TI__Guru* 96591 points

    Hi Pengfei,

    V_IH and V_IL are not input threshold values, but are guaranteed input HIGH or input LOW levels.  For an input signal at 3.3V operation, from 0V to 0.8V, the device sees this signal as a LOW. From 0.8V to 2V the input is UNDEFINED, and from 2V to 3.3V, the input is HIGH.

    There is also an FAQ on this topic located here:

     

    Please let me know if this resolves your issue by clicking the green "This resolved my issue" button, or respond if I can be of further assistance.

  • 0 in reply to Emrys Maier
    TI__Intellectual 2035 points

    thanks for your reply. So, if my input voltage is 2V. how to define this voltage level? high or undffined?

    Thanks

    -Pengfei

  • 0 in reply to Vincent Li00
    TI__Guru* 96591 points

    Operating your system with an input at exactly 2.000000 V is a bad idea -- mostly because I have never seen a system with zero noise and zero ringing, so the input would invariably go below 2V into the 'undefined' region.

    If you do have a magic system that holds 2V perfectly, then the input would be considered HIGH.

    I would still not recommend operating the input at 2V though, for the same reasons you shouldn't have slow inputs on CMOS devices as described here:

     

    Pulling the input voltage away from the rails will cause added current consumption that is completely unnecessary. Note that ΔIcc is measured at Vcc - 0.6V, and already has a maximum of 500uA. Operating the input at Vcc - 1.3V (ie 2V) will cause extra supply current in the ~10mA range.

  • 0 in reply to Emrys Maier
    TI__Intellectual 2035 points
    OK. Got it. Thanks Maier.
    -Pengfei