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SN74HCU04: VIH at VCC = 3.3VDC ?

Ishan Panchal
Intellectual 640 points
Part Number: SN74HCU04
Other Parts Discussed in Thread: SN74LVC1G08

What is the VIH level for VCC = 3.3VDC ? I plan to use this part as a part of SPDIF to Optical audio converter. The SPDIF level is 3.3V. Even if I give a VCC = 5VDC then also the SN74HCU04 won't consider it as high because for VCC= 4.5VDC the VIH level is 3.6VDC.

Thanks,
Ishan

  • 0
    TI__Guru* 96822 points

    Hi Ishan,

    There are two FAQ's that I would recommend for you, located here:

     

     

    If these answer your question, please come back and mark this "resolved" to help others find these answers.  If not, please respond and I do my best to help.

  • 0 in reply to Emrys Maier
    Intellectual 640 points

    Hi Emrys,

    Thanks for the quick response..!!!

    I referred the two FAQ's suggested by you.

    FAQ1 is related to device not switching at VIH/VIL, while in my case I don't know VIH at 3.3VDC. The example part SN74LVC1G08 in FAQ has a detailed VCC description for VIH and VIL. But if you refer the datasheet of SN74HCU04, the 3V level is not displayed for the VIH and VIL values.

    FAQ2 shows interpolation method to estimate the values but if I use your example sheet the values are not quite satisfactory. This is because the VCC range given in the example sheet is from 3 to 4.5 while in SN74HCU04 datasheet the VCC range for VIH/VIL is from 2 to 6 V.

    What I suggest that you should add the 3 to 3.6V range in the SN74HCU04 datasheet just like SN74LVC1G08. This will make it clear if the SN74HCU04 will switch at 3.3V input levels or not.

    Regards,
    Ishan

  • 0 in reply to Ishan Panchal
    Intellectual 640 points
    For now I will stick to the rule of 0.7Vcc for VIH and 0.3Vcc for VIL.
  • 0 in reply to Ishan Panchal
    TI__Guru* 96822 points
    Alex,
    The values in that spreadsheet can be changed -- you don't have to use 3V to 4.5V... that's just an example.

    I would highly recommend interpolating the values. We won't be adding these values to the datasheet -- the method used for characterization has been in place for more than 40 years and is the industry standard.
  • 0 in reply to Emrys Maier
    Intellectual 640 points

    Hi Emrys,

    I did changed the VCC values in the spreadsheet but then they doesn't match the values in the datasheet. There was a difference of 0.22v for VCC = 2V for VIH.

    Anyways I would test the chip practically when I have it.

    Thanks..!!!