• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 19 subscribers
  • Views 704 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.

1.8 to 3.5/5 Volt level translation

Ted Mawson 3.0
Expert 1795 points
Other Parts Discussed in Thread: TXB0102

Hi,

I have a board with a microcontroller running at 1.8 volts. I want to be able to connect an external serial connector that runs at 3.3 or 5 volts.  I am considering the TXB0102 with the 1.8 volt side connected to A and the 3.3-5.0 volt external side connected to B.

The issue is that the external serial connection - along with the 3.3-5.0 volts supply - may not always be there and that would violate the rule that Vcca should not exceed Vccb because when the external serial is disconnected, Vcca will be 1.8 volts and Vccb will be zero.

If I connect OE to ground using maybe a 10k resistor and then have OE pulled up by the external supply, when it's connected i.e. OE is connected to Vccb, will that still violate the rules of this device? If yes, what do you recommend?

Thanks

  • 0
    TI__Expert 6335 points

    Ted,

    I believe that your application is ok. Vcca or Vccb = 0V is a special circumstance that does not violate the Vcca <= Vccb rule.

    The TXB0102 has a feature called "VCC isolation" (mentioned in the 'Features' section). This means that if either Vcca or Vccb is at 0V (to be more specific, less than 0.4V), then the outputs are high impedance.

    Since your application will keep Vccb at 0V when the external serial is disconnected, then you will be ok.

    We have an app note for our TXB devices that goes into detail on VCC isolation mode. Section 4 [Output Enable Control] has the details.

    Best Regards,
    Nirav

  • 0 in reply to Nirav Patel
    Expert 1795 points
    Nirav, I like what you proposed, are you assuming that my 10k ohm resistor is what takes Vccb to 0 volts and do you think that resistor is required?

    Thanks

    Ted
  • 0 in reply to Ted Mawson 3.0
    TI__Expert 6335 points
    Ted,

    Based on your initial post, I am assuming that the system is designed to hold Vccb to 0V when the external serial is disconnected. Is that correct?

    The VCC isolation feature is actually indepedent of the OE pin state. Just don't leave the OE pin floating. OE is typically tied to VCCA through a pullup resistor.

    Best Regards,
    Nirav