• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 18 subscribers
  • Views 141 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.

TXB0104: Question on Protection

Mitchell
Expert 4915 points
Part Number: TXB0104
Other Parts Discussed in Thread: SN74AXC4T774

Hi Team,

My customer is working with the TXB0104 level shifter for SPI in a new design. In this case the VCCB rail is switched on and off periodically while the VCCA rail is always on. The OE pin is connected to a voltage divider connected to VCCB. The voltage divider shifts VCCB (3.3V) to the VCCA voltage level (1.8V).

In the static "ON" case the design obeys the requirement that VCCB (3.3V) > VCCA (1.8V).

They saw the note in section 10 in the TXB0104 datasheet that suggests that the device is protected during power-up even if VCCB < VCCA. Would that protection be sufficient in the case where VCCB powers up and down multiple times?

What type of failure modes might we expect to see, if not?

Is there any sort of undervoltage protection on the VCCA/VCCB rails, if there were to be a slow ramp down on the VCCB side?

Thanks!
Mitchell

  • 0
    TI__Guru 56220 points

    Hi Mitchell,

    I would suggest to consider using the SN74AXC4T774 for SPI level translation in your case.

    The AXC4T774 doesnt have the restriction on the power supplies like the TXB0104 does.( Vcca <= Vccb)., and hence can be used for level translation (during normal operation ) and isolation( during Vccb off)..

    This devices also features Ioff protection which ensures that you can have IO signals on the ports with either one of the supplies turned off without additional leakage or accidentally power on the device.

    TXB0104 requires Vcca <= Vccb during normal operation which as you have mentioned can be violated during power on. however, we cannot guarantee if this Vccb is being switched on / off regularly. There is internal diode between the supplies which activates when Vcca > Vccb.