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SN74LVC1G125: For the route from output to VCC.

Kengo.Y
Guru 10615 points
Part Number: SN74LVC1G125
Other Parts Discussed in Thread: SN74LVC1G07,

Hi team,

Voltage was seen at VCC even when power was not applied to VCC when there was power on the output side pull-up.
Is there a path for current to flow from the output to VCC?




Sincerely.
Kengo.

  • 0
    Guru 267960 points

    Section 9.3 of the datasheet says that the "Ioff feature allows voltages on the inputs and outputs, when VCC is 0 V".

    Is VCC 0 V, or is it floating (with some remaining charge on the decoupling capacitors)?

    If you do not need fast rising edges, an open-drain device like the SN74LVC1G07 might work better in this application.

  • 0 in reply to Clemens Ladisch
    Guru 10615 points

    Thank you for your comments.

    I understood that this was due to the Ioff function.
    Vcc is used as a pull-up power supply for another circuit.
    Therefore, it is open or 0V when the　VCC is power off.
    In the bellow circuit, there is a protection diode on VCC, so I don't think any current flows from Vout to VCC.
    Please let me know what path is being followed for this phenomenon.



    Sincerely.
    Kengo.

  • +1 in reply to Kengo.Y
    Guru 267960 points

    When the SN74LVC1G125 drives it output high, there is a path between the output and VCC. (And when /OE is low and VCC is below the recommended minimum of 1.65 V, correct operation is not guaranteed.)