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TXS0108E: TXS0108E I2C/UART/GPIO application

Part Number: TXS0108E
Other Parts Discussed in Thread: SN74AVC4T774, SN74LVC1T45

Hi Team,

I plan to use the TXS0108E in my EVM board to transfer the voltage level between MCU controller and the device IC. 

Here i have 3 questions,

1. i will not control the OE pin, should i connect it to VCCA or GND? I am confused by the related description in the datasheet. From my understanding the I/O pins should be in Tri-state output-mode.

2. This IC can be used in UART communication case?

3. Does this IC support constant level transfer? For example, constant 3.3V (high) input transferred to constant 5V (high) output.

Thanks and best regards,

Felix

  • Hi Felix,
    1. OE means "Output Enable" and should be held HIGH to Enable the Output. If you want the device disabled, you would hold this pin LOW. I agree that the text there is a bit confusing. I'll make a note to update it in the next d/s revision.

    2. Yes. It will depend on the data rate, but in general, this device can be used for UART. I would actually recommend a different device for most cases since auto-bidirectional translation isn't really required for UART. An example would be the SN74AVC4T774

    3. Yes. Note that the output will have _very_ limited drive strength in this case -- ie you can't drive something like an LED from the TXS, but you can send a signal at 5V. If you need up translation with stronger drive strength, look into the LVCxT family of translators (ex: SN74LVC1T45)
  • Hi Emrys,

    Thanks for your answer.

    1. As mentioned in the Datasheet, is it better to tie OE to GND through a pull-down resistor while holding HIGH? 100k can work?

    2. The highest date rate would be 1Mbps. Thanks for your recommendation. But i need to transfer 3V logic to 5V logic.

    3. I think i don't need it has very much output driver strength.

    Following is my application, could you help to have a check to see if there will be any potential issue? Or any suggestions?

    Thanks and best regards,

    Felix

  • Holding the OE pin down with a pull-down resistor is only required if you need it to be low on startup, then overdrive with an MCU or other signal. The pull-down is just using power in the above schematic (unless 3.3V is floating at some point?)

    1Mbps 3V to 5V won't be a problem for the TXS0108E

    The TXS contains 10kohm pull-up resistors. The external 47kohm pull-up resistors are not required. The 4.7kohm can be used if you want a stronger pull-up, but it can also likely be removed.
  • Hi Emrys,

    1. Yes, in some case, user may skip the TXS0108E to communicate with the devide directly. Then i thought user could just left the 3.3V floating to make all the pins in High-Z state.

    2. In the case the TXS0108E is skipped, I'd like to keep the TX/RX (from device) pulled up with the external 47k resistors. Will these 47k pull up resistors influence the function while TXS0108E is working?

    Thanks and best regards,

    Felix

  • It's the other way around -- the 10kohm internal resistors will reduce the pull-up value to about 10k (47k || 10k = 8.25k). These resistors are not disconnected by the 'OE' pin.