• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 21 subscribers
  • Views 520 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

SN74AXC8T245: Output after VCCA lost power

Hao Wang14
Expert 4415 points
Part Number: SN74AXC8T245

Hi Team,

The datasheet says: The VCC isolation feature ensures that if either VCC input supply is below 100 mV, all level shifter outputs are disabled and placed into a high-impedance state.

Here is the application: 1.5V is for processor and VCCA, 3.3V is for VCCB.

In the beginning,  /OE is connected to GND, A1 is input and B1 is output. Processor is set to high on A1, so B1 is high.

Then /OE is connected to 1.5V, when 1.5V for processor and VCCA powers off, what will B1 be? Is it still keeps high?

What does the figure 4 mean in the datasheet?

Thanks and best regards,

Hao

  • 0
    Guru 317000 points

    When the OE input is driven high, or when at least one VCCA/B is off, then all outputs are disabled. If there isn't another device driving that signal, and if there is no pull-up or pull-down resistor, then the output will be floating.

    Figure 4 shows the timing of an output that is being disabled, and that is pulled by a resistor in the opposite direction than it was being driven (see figures 1/2).

  • 0 in reply to Clemens Ladisch
    TI__Guru 62180 points
    Thank you, Clemens for your input on this.
    Hao,
    If there is anything else, please let me know.