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SN74LV08A Protection

hj
Intellectual 650 points
Other Parts Discussed in Thread: SN74LV08A

I am using the SN74LV08A gate to protect a processor from voltage while not powered.

If there is no voltage on VCC, is it harmful for this part (SN74LV08A) to receive a voltage on one of the inputs? (1A, 2B, 2A, 2B, 3A, 3B, 4A, 4B) The data sheet states that the input voltage range is -.5V to 7V. Does that include when VCC is off too?

Also, if there is no voltage on VCC, is it possible to have any accidental voltage on the outputs (1Y, 2Y, 3Y, 4Y) if a voltage is supplied on the inputs? (1A, 2B, 2A, 2B, 3A, 3B, 4A, 4B)


Thanks

  • 0
    TI__Genius 9860 points
    Hi hj,

    Yes, it is OK for voltage to be applied to either the input, output, or both when VCC = 0. This is because of the "IOFF" feature mentioned on the first page of the datasheet. You can read more about IOFF on page 5 of the application report here: www.ti.com/lit/pdf/szza033

    The fact that the input and "voltage applied to output" ranges go from -0.5 to 7 V indicate it is safe. Otherwise, we specify the maximum as VCC + a voltage (usually 0.5V).

    What application are you using the device in where undesired voltage is present?
    -Ryan
  • 0 in reply to C. Ryan Land
    Intellectual 650 points
    Thanks. It is for collecting a logic input from an outside device. (3.3V/0V) I just want to make sure this part will be fine if the external device is powered on while my device is not.

    A 3.3V may be present on an input for the gates. I just want to make sure the outputs will not pass the 3.3V unless VCC is powered