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SN74LVC1T45: SN74LVC1T45 and TXB0108, TXS0102 connection

Part Number: SN74LVC1T45
Other Parts Discussed in Thread: TXB0108, TXS0102, SN74LVC2G34, SN74LVC1G34, SN74LVC3G34, SN74AHC1G125

I have a question about the interface of 3 devices connected to UART.
Device A's I/O control is done by FPGA, and it processes UART TX and RX signals of devices B and C.

I am trying to connect FPGA and Device B (or Device C) by using the non inverting buffer SN74LVC1T45.
Device B inputs/outputs 3.3V level UART signals with TXB0108 chip, and device C inputs/outputs 5V level UART signals with TXS0102 chip.

I want to use SN74LVC1T45 buffer as below.


In this case, the buffer can drive the TXS and TXB chips with sufficient current, and is there any problem with UART communication?

Or, please introduce a chip that can be used instead of SN74LVC1T45.
Devices B and C have already been manufactured, so it is difficult to change the TXS and TXB chips.

Thank you in advance.

Best regards.

  • Yes, LVC buffers are appropriate for this application.

    3.3 V to 3.3 V does not need a translator; simply use the SN74LVC2G34.

    Converting 5 V to 3.3 V can be done with any buffer with overvoltage-tolerant inputs, such as the SN74LVC1G34. (Or use the SN74LVC3G34 to combine it with the other ones.)
    Converting 3.3 V to 5 V can be done with any buffer with TTL-compatible inputs, such as the SN74AHC1G125.

    If you want to simplify your BOM, you could use 4× SN74LVC1T45.

  • Hello,

    Clemens is correct, however it seems to me that this system may be a bit over-engineered.

    For FPGA to device B communication, why not communicate directly to the TXB0108?

    For FPGA to device C communication, why not eliminate all the translators and communicate directly?

    I'm wondering if these are physically separated systems -- ie is there a cable running from device A to the other two devices in these two locations?

  • Hello, Thank you for reply.

    For FPGA to device B communication, why not communicate directly to the TXB0108?

    For FPGA to device C communication, why not eliminate all the translators and communicate directly?

     

    → We just want to connect the SN74LV1T45 as a buffer to protect the FPGA.

    I'm wondering if these are physically separated systems -- ie is there a cable running from device A to the other two devices in these two locations?

     

    →  Yes, Device A, B and C are seperated physically. Actually, Device A is FCC in drone, B is image processing uint, C is Datalink system.

    The connection diagram of devices A and C was redrawn as shown below because there were some errors in the picture presented above.

  • Hi, Thank you for reply.

    I wanted to use the LVC buffer to protect the FPGA.
    And I wanted to transfer sufficient current driving from TXS and TXB chips to FPGA using LVC buffer.

    Is it suitable for this purpose?

    Thanks in advacne.

  • Yes, LVC can buffer such signals.

    Please note that TXS and TXB devices can have problems with nontrivial loads; the distance between the buffers and the TXB/TXS devices should be as short as possible.