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TXB0104: UART can't be work using TXB0104

Part Number: TXB0104
Other Parts Discussed in Thread: TXU0204

I used TXB0104 for 3.3V UART translate to 1.8V.

However, the UART can't be workable. UART signal is only high or low. Even I added the external P/U resistor 5k ohm or 50k ohm, it still can't work.

I changed the level shift IC from TXB0104 to TXS0108, and then the UART function is workable.

The application of TXB0104 is also suggested for UART. I can't understand why it can't be applied.

  • The TXB is an auto-bidirectioal translator and has many restrictions; see section 8.3 of the datasheet. You have not shown the schematic, but I guess that your circuit does not conform to these restrictions.

    For unidirectional signals, you should use a unidirectional translator like the TXU0204.

  • However, for the application suggestion of TI, it mentioned that TXB0104 can be applied for UART.

    Besides, why can TXS0108 be workable even TXS0108 is also applied for bi-direction signal?

    Could you explain what's the concern if TXB0104 use for unidirection signal?

  • The circuit is as the following picture.

  • Hi Tommy,

    Do you mean the TXB device is not switching but staying high/low i.e static but TXS is switching from high to low?

    I would recommend to double check BT2 do not have internal pull ups / pull downs as the TXS may work better with pull-ups for higher VOL levels.

    If not the case, I would further recommend replacing with a known good TXB to help double check if any damages. If needing more information, please also help provide waveforms from both devices to help clarify while also ensuring bypass caps are used with Vcc supplies, thanks.

    Best Regards,

    Michael.

  • The weak outputs of the TXB work only for short traces, and without pull-up/-down resistors. (The schematic does not show whether there are additional componentes connected to the UART lines.)

    The TXS works only at relatively slow speeds, and has open-drain outputs. In application where these characteristics work, it is more robust than the TXB.

    The latest TI recommendations suggest the TXU0204 for UART signals. (The TXU devices are rather new; there might be older information out there.)