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TXS0108E: I2C low level up to 0.6V or even higher

yuchen.qin
Prodigy 40 points
Part Number: TXS0108E
Other Parts Discussed in Thread: TCA9800, TS5A23159

Tool/software:

We use TXS0108E as a 1.8V to 3.3V level shift，we found that no matter what external pull-up resistor we use，the low level of the 3.3V could be up to 0.6V or even higher. How much is the internal pull-up resistor? How can we lower the low level to less than 0.4V.

  • 0
    Guru 316920 points

    The internal resistors are 40 kΩ when driving low. You should not need any external ones.

    The TXS is a passive switch; the low-level voltage depends on the drive strenght of the other devices.

    Why are you using an eight-channel device? Do you have four I²C buses? For a single I²C bus, you could use an I²C buffer like the TCA9800.

  • 0
    TI__Mastermind 40606 points

    Hi Yuchen,

    Clemens' is correct here, the TXS0108E has internal pullups already, and with the inclusion of external pullups, it will result in a voltage divider yielding higher VOL levels. It is further documented on this app note. 

    Regards,

    Jack

  • 0
    Prodigy 40 points

    We remove the external resistors and find that there is no help. We use txs0108e for HDMI I2C buses, we have three buses on the board.  

    And the signals will go through a mux TS5A23159 then go to the carrier.

  • 0 in reply to yuchen.qin
    TI__Mastermind 40606 points

    Hi Yuchen,

    Can you confirm that external pullups between TXS0108E and TS5A23159 are also removed (R171-R177 as well as R165 and R167)? Are there pullups internal to the driver on 1V8 side? 

    Regards,

    Jack