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Original question:

TXS0108E: Does TXS0108E support UART level conversion

TXS0108E: Needed help for "higher" current drive capability replacement

Adam Alfath
Prodigy 10 points
Part Number: TXS0108E
Other Parts Discussed in Thread: SN74LVC8T245, TCA9517, TXU0304, SN74LXC8T245, TXU0204, TXU0104, PCA9306, TCA9803

Currently I'm using 2x TXS0108 as LLC from 3.3V level MCU to 5V (VDD) level peripheral for 1xI2C, 2xUART, 1x1-Wire, and 7 output only signals (on 2nd IC).

Unfortunately it's not working reliably. From what I observe:

  • the I2C is working fine
  • 1-Wire is not tested yet
  • UART peripheral TX -> MCU RX, MCU receiving garbage message
  • UART MCU TX -> peripheral RX, peripheral receiving correct character
  • UART and the output signal voltage at idle are dropped to around 3V.

The TXS datasheet stated that it only has several uA drive capabilities (not really driving capable). Assuming the peripheral needed in the order of 1-5mA current input, my question is:

  1. Is it correct that this behavior is caused by the translated voltage getting overloaded resulting in the voltage drop and signaling issue?
  2. For the output-only signal, I'm considering replacing the IC with SN74LVC8T245, is it the correct choice?
  3. Is there an option for TSX replacement for I2C, UART & 1-Wire with higher current drive capability? I don't mind if the translator IC needed to be separated considering UART is unidirectional and I2C/1-Wire is bidirectional.

Thank you.

  • +1
    Guru 243180 points

    The TXS has open-drain outputs, so it cannot source much current.

    I²C and 1-wire use open-drain signals, so the TXS should be OK. The TXS is a passive switch, so you could consider an I²C buffer like the TCA9517.

    For the other signals, you should use a buffered translator like the SN74LVC8T245/SN74LXC8T245 or TXU0104/TXU0204/TXU0304.

  • 0 in reply to Clemens Ladisch
    Prodigy 10 points

    Thank you for your quick reply and suggestion. The part mentioned indeed satisfied my requirement, I will use SN74LVC8T245 for the general output signal. Unfortunately TCA9517 & TXU series it's non stocked at my nearest distributor but I found TCA9803 & PCA9306.

    1. Can it be used for all the communication signals? (I2C, 1-Wire, UART, assumption 1mA<=Iox<=3mA)
    2. What is the definition for pass current switch (Ipass) and continuous channel current mentioned on the TCA & PCA datasheet?

    Thank you.

  • 0 in reply to Adam Alfath
    Guru 243180 points

    The TCA9803 and PCA9306 are designed for I²C, and have open-drain outputs.

    All the translators I've mentioned are available directly from TI.