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TXS0108E: I2C communication using TXS0108E

yamamotoju
Prodigy 130 points
Part Number: TXS0108E 
I have a question about the TXS0108E 8-Bit Bi-directional, Level-Shifting, Voltage Translator.
In our circuit, we use TXS0108E for the I2C communication line to change the level, but depending on the pull-up resistor value, abnormal oscillation will occur in the signal.
(See file: 20240325_Circuit_and_waveform.jpg)
(1).The TXS0108E is said to switch the direction of the signal automatically, but I am looking for documentation explaining its operation.
Will the port side where the voltage changes (L→H or H→L) be judged as the input port and the other side will be switched to the output port?
(2).What are the possible causes of oscillation?
  • 0
    Guru 275410 points

    The TXS does not really detect the direction; the circuits on both sides are always active.

    Oscillations are usually caused by ringing that is amplified by the TXS's edge accelerators. Do you have long traces, connectors, or cables?

  • 0
    TI__Mastermind 24781 points

    Hey Yamamotoju,

    External pullups are no longer needed for this device and can be removed since the TXS translators have internal 10kohm pullups. 

    1. The device is open-drain based.  For any input signals lower then VCC, the low signal will be propagated to the output as logic low with the internal switch acting as a resistor. Similarly for input signals near VCC, the switch will be open and a high state is achieved on the outputs. One shot circuitry is also included to provide faster transition times during a L-> H and H-> L. You can see more on its operation here in this app note: A Guide to Voltage Translation With TXS-Type Translators

    2. It could be the one shot circuitry being retriggered by accident. Please ensure proper ground connections and the output cap. loading is kept to a minimum. 


    Regards,

    Jack 

  • 0 in reply to Jack Guan
    Prodigy 130 points

    I delayed to reply.
    >Oscillations are usually caused by ringing that is amplified by the TXS's edge accelerator. Do you have long traces, connectors, or cables?
    ⇒Are there any length regulations? (For example, 200mm or less...etc.)
    In this experiment, we were able to reproduce the oscillation phenomenon, but when the pull-up resistance value on the CPU side becomes low, the oscillation phenomenon occurs.
    When the VIL on the A port side increases and the VOL on the B port side exceeds 0.15V, the original B→A signal transmission repeats B→A→B→A... I think that a one-shot circuit is working, but is such behavior possible?

  • 0 in reply to yamamotoju
    TI__Mastermind 31515 points

    Hi Yamamotoju,

    Yes, please see  Leveraging Edge Rate Accelerators with Auto-Sensing Level Shifters mentioning about 64 mm dependent on your design factors.

    Also, yes pull-ups impacts the switching levels, with the referenced app note further clarify your concerns, thanks.

    Best Regards,

    Michael.