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SN74CB3T3384 - Supply voltage behavior

Other Parts Discussed in Thread: SN74CB3T3384

Hello,

I need some advise concernig the SN74CB3T3384 and its behavior at different Vcc levels.
All facts are taken from datasheet sn74cb3t3384.pdf

On page 2 Note A says:

"If the input high voltage (VIH) level is greater than or equal to VCC − 1 V,
and less than or equal to 5.5 V, the output high voltage (VOH) level
will be equal to approximately the VCC voltage level."

The simulations are taken from page 8 (Vcc=2.3V and Vcc=3.0V, minimal load Io=1u)

Here the output level does not reach full Vcc right after Vcc - 1V. It is about 0.25V below Vcc.















For my application its essential to get an Vout_max of 2.5V @ Vin=2.0V - 3.3V.

So the optimal Vcc for that must be in between 2.3V and 3.0V.
Is it save to interpolate and set the supply to Vcc = 2.5V + 0.25V = 2.75V ?

Thanks for your advice.

  • Unfortunately the datasheet is wrong.

    "If the input high voltage (VIH) level is greater than or equal to VCC − 1 V,  (This statement is wrong).

    It should read
    If the input high voltage (VIH) level is greater than or equal to VCC + 1 V

    Thes part are actually designed to translate down. The input should be 1V greater than Vcc for the output to reach Vcc. If the input is not 1V greater than Vcc it can be pulled the rest of the way by a pullup resister.

    If you are translating down from 5V to 3.3V. input 5V  and  vcc 3.3V the part will work fine. or 3.3V to 2.5V it will work fine. If you are going from 2.5V to 3.3V you will need a pullup resistor to get the output to 3.3V.

    I will get the datasheet corrected.