• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 21 subscribers
  • Views 586 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.

SN74LVC8T245: Questions for SN74LVC8T24-urgent!

Sulyn ZHANG
Expert 8700 points
Part Number: SN74LVC8T245

Hi Team,

My customer have urgent question for SN74LVC8T245 that I can't find from datasheet, could you pls help double check, thanks! Questions as below:

1. If DIR=VCCA(Data from A to B), if VCCA off, what will be the I/O status of A side and B side separately? High/Low or High impedance?

2. If DIR=VCCA(Data from A to B), if VCCB off, what will be the I/O status of A side and B side separately? High/Low or High impedance?

3. If DIR=GND(Data from B to A), if VCCA off, what will be the I/O status of A side and B side separately? High/Low or high impedance?

4. If DIR=GND(Data from B to A), if VCCB off, what will be the I/O status of A side and B side separately? HIgh/Low or high impedance?

I see this part support Ioff function, can you help double check, thanks!

Best regards,

Sulyn Zhang

  • 0
    TI__Mastermind 30815 points
    Hello Sulyn,

    If either VCCA or VCCB is at ground, all I/O pins will be in a high impedance state. This is independent of the status of the DIR pin, or any other control pins. Please be aware that the Ioff function only applies if the supply is at GND. If the supply is turned off and left floating, the Ioff feature cannot be guaranteed and you may see higher power consumption than expected.
  • 0 in reply to aozer
    TI__Expert 8700 points

    Hi aozer,

    Thanks a lot for your support! About the Ioff, you mentioned "Please be aware that the Ioff function only applies if the supply is at GND. If the supply is turned off and left floating, the Ioff feature cannot be guaranteed and you may see higher power consumption than expected." , here I'm confused by the "supply is at GND" and the

    "supply is turned off", what's the difference here?

    BTW, for the supply is at GND, do you mean either VCCA or VCCB?

    Best regards,

    Sulyn Zhang

  • 0 in reply to Sulyn ZHANG
    Guru 317370 points
    "At GND" means that there is some connection to ground, so that the voltage difference between VCCx and GND is guaranteed to be zero.
    "Floating" means that there is no connection.

    What happens in your circuit depends on how your power supply is actually implemented. If the supply is disconnected mechanically, then there is no connection; consider using a weak pull-down resistor in that case.

    (VCCA and VCCB are symmetrical.)