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TXB0104: Level Shifter Change

Suyoung Kwon
Prodigy 20 points

Part Number: TXB0104
Other Parts Discussed in Thread: TXU0204, TXU0304, TXS0104E

Hello.

I have an inquiry regarding level shifters.

I have currently designed a circuit using the TXB0104 (see Figure 1 - No pull-up resistors used for input/output). I am sending this email to confirm whether there will be any issues with the circuit's operation if I replace it with the TXS0104.

Please reply after reviewing this.

image.png

(Figure 1) TXB0104 circuit

 

  • 0
    Guru 326180 points

    The TXS has internal pull-up resistors. I do not know how this will affect your circuit.

    The signals appear to be unidirectional; consider the TXU0204 or TXU0304 (with a different pinout).

  • 0 in reply to Clemens Ladisch
    Prodigy 20 points

    There is a phenomenon where B1 operates upon power-on, outputting a low signal to A1. We expect that using TXS will eliminate this low behavior of A1 due to its internal pull-up resistor. Therefore, we need to verify if using TXS instead of TXB is acceptable. We require an alternative solution for this unwanted behavior when power is initially applied.

    We are unable to modify the PCB or circuitry. (Component replacement is possible.)

  • 0 in reply to Suyoung Kwon
    TI__Guru 60891 points

    Hi Suyoung,

    Please note that the device's internal pullups are only active when the device VCCA/ VCCB is powered up. The device that Clemens' recommended (TXU0x04) is also a viable solution, and external pullups can be placed at the I/Os to ensure a default logic high state.

    Regards,

    Jack

  • +1 in reply to Jack Guan
    Prodigy 20 points

    It needs to operate only once when power is applied. The important thing is that the A-port must go high when power is applied. The TXU0x04 you recommended has an internal pull-down resistor, so it appears that the A-port might go low when power is applied. (Adding an external pull-up resistor is not possible.)

    What I want to know is whether there are any circuit issues if I use TXS instead of TXB. If there are no problems with the substitution, I plan to use TXS.

  • 0 in reply to Suyoung Kwon
    Guru 326180 points

    The TXS0104E pulls it outputs high by default. It works as a passive switch, so an output can go low only when an external device pulls the input pin low. As far as I can see, this is exactly what you want.

  • 0 in reply to Clemens Ladisch
    Prodigy 20 points

    Thank you for your cooperation