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SN74LVCC3245A: ViL, ViH, VoH,VoL

Xiao Zhu2
Expert 3215 points
Part Number: SN74LVCC3245A
Other Parts Discussed in Thread: SN74LV8151

Hello Team

 I am confused the ViH, ViH. My understand is: When the input higher than the 3.85V, the Vo will change to high， when the Input chang from 3.85V to 0.2 V， the Vo will change to low.  But when we use it and test it , the Vo will change high or low at about 2V, so could you help explain about it? thanks

  • 0
    TI__Guru* 97017 points

    Hi Xiao,

    The confusion here is in terminology. The "Input-high voltage" (VIH) is the minimum value at which a device will be guaranteed to see the input voltage as a logic 'HIGH'.

    The value at which the device switches is identified as the "Input threshold voltage" (VT) and is not specified in most logic device datasheets. It is typically around 1/2*VCC for CMOS devices, but can differ because of design.

    Note that there is also a specification of input transition rate in the Recommended Operating Conditions table -- the threshold value shouldn't really make a difference in operation if the input transition rate is being properly observed.

    If you would like to learn more, these values are clearly defined in the TI Application Report, Understanding and Interpreting Standard-Logic Data Sheets on pages 28 and 35.

  • 0 in reply to Emrys Maier
    TI__Expert 3215 points
    Hello Emrys
    Thanks for your replay. It is very useful to me. Do we have some product which will have product which have difference threshold value? because when the input voltage rise up slowly, when some noise at input, the output will be oscillate.
  • 0 in reply to Xiao Zhu2
    TI__Guru* 97017 points
    Yes and no - what you are looking for is a Schmitt-trigger input device. We definitely have Schmitt-trigger input devices, however we do not currently have a Schmitt-trigger input device that perfectly matches the functionality of the SN74LVCC3245A.

    Are all channels slow inputs or just one or two?

    Will the direction of the channel with slow inputs change, or is it fixed?
  • 0 in reply to Emrys Maier
    TI__Expert 3215 points
    All the channel. the direction is fixed in this application
  • 0 in reply to Xiao Zhu2
    TI__Guru* 97017 points
    In that case, you might consider using SN74LV8151, which is a Schmitt-trigger buffer device with 8 channels that can be 3-stated, and an extra buffer/inverter that are not 3-statable.