• State Answer Suggested
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 19 subscribers
  • Views 1738 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

When SN74LVC1G07 power off, the output have ground bound

Thomas Chang15933
Expert 4770 points
Other Parts Discussed in Thread: SN74LVC1G07, SN74LVC1G17

Dear Team:

 Our customer used SN74LVC1G07, but got seems gound bound at output, when Power off.

As below is their circuit and waveform. Second 2 picture is Zoom in picture.

  • 0
    Guru 295240 points

    What do the four inputs measure? Which power was switched off? Is there really no decoupling capacitor?

  • 0 in reply to Clemens Ladisch
    TI__Expert 4770 points
    Dear Ladish:
    Four input measure: Scope 4 color signal waveform (P3V3STBY, P3V3, FM_M2_SSD_PEDET, FM_SSATA_PCIE_M2_SEL). Both power turn off happened the issue.
  • 0 in reply to Thomas Chang15933
    Guru 295240 points

    Sorry, I overlooked these labels.

    The Ioff feature of this device works when the power is switched off. However, the power supply for this device is P3V3_STBY, which stays up.

    Switching off P3V3 affects only the input signal, and with the slow decay shown above, the input signal violates the input transition fall time (Δt/Δv in table 6.3 of the SN74LVC1G07 datasheet). Oscillations are expected to happen when you do that; see Implications of Slow or Floating CMOS Inputs (SCBA004).

    You should connect the buffer to the power supply that is always switched off first. If that is not possible, use a buffer with a Schmitt-trigger input (e.g., SN74LVC1G17, with a push/pull output).