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Original question:

TXB0108: lock B4 to High

TXB0108: About external pullup and Pulldown when an FPGA has internal Pullup resistance

Yuta Nishie
Genius 4985 points
Part Number: TXB0108
Other Parts Discussed in Thread: TXU0304, TXU0104, TXU0204

Hi,

There are two cases where the initial voltage of the device connected to Ax of TXB0108 must be set to High and Low.
Also, an internal pull-up resistor of 15 kΩ to 30 kΩ is connected to the FPGA.

1. When it is High.
1.1. Is the circuit OK with the image below?
1.2. Which resistance value is better for A and B: 100 kΩ, NC or X kΩ (please tell me your recommended value)?

2. When it is High.
2.1. Is the circuit OK with the image below?
2.2. Which resistance value is better for A and B: 100 kΩ, NC or X kΩ (please tell me your recommended value)?

3. Is it correct that 1.8V is applied to the OE after the Device is power-up?

Best Regards,

Nishie

  • +1
    Guru 316780 points

    To allow bidirectional signals, the TXB's outputs have an extremely low drive strength. So they do not allow pull-up/-down resistors stronger than 50 kΩ.

    It is not possible to use the FPGA's internal pull-up with the TXB.

    For unidirectional signals, use a unidirection translator like the TXU0104/TXU0204/TXU0304.

  • 0 in reply to Clemens Ladisch
    Genius 4985 points

    Hi Clemens-san,

    Thank you for your reply.

    I understand.

    Let me make an additional confirmation.

    Is my understanding below correct?

    1. When using the internal pull-up of the FPGA, the TXB series can not be used even with didirectional signals.

    2. When not using the internal pull-up of the FPGA, the TXB series can be used even with unidirectional signals.

    Best Regards,

    Nishie

  • +1 in reply to Yuta Nishie
    Guru 316780 points

    Yes. (Only the value of the pull-ups/-downs matter.)