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TXB0104: Throughput of TXB0104 & TXB0106

Part Number: TXB0104
Other Parts Discussed in Thread: TXU0304, TXU0104, TXU0204, TXU0202, TXU0102, TXS0108E, TXS0104E, TXS0206, TXS0102, SN74AXC8T245, SN74AXC4T774, SN74AXC4T245


In one of our FPGA board designs, we have to use voltage converters to connect a few UARTs (RS-232 and RS-422 ) interfaces, as the FPGA bank voltages and external Transceiver voltages are not matching . We need a throughput of around 1Mbps (921 kbps) for these UARTs.

Ours is a very small form factor and low power design.

Some places we need 6 nets and few other 4 nets to be voltage converted. We were planning to consider TXB0104QPWRQ1, TXB0106PW for voltage conversions from 1.8V to 3.3V Can you confirm if these parts support 921kbps speed. Are there any better small form factor devices that are meant to be used as UART signals level converters at a speed of 921 kbps.


  • TXB are designed for bidirectional signals, and thus have many restrictions and limitations.

    What are the voltages and directions?

    UARTs use unidirectional signals; consider the TXU0104/TXU0204/TXU0304/TXU0102/TXU0202.

  • We are using 1.8V to 3.3V conversations  and also 1.2 V to 3.3 V conversations. Instead of auto direction parts we can also consider unidirectional parts as well. We need only Tx & Rx signals to be considered, but combining multiple ports together we need 2 port, 4 port and 6 port options ( as there are 6 stacked-up boards and these interfaces are spread across multiple boards )

  • How many in each direction? (The TXU parts will work.)

  • As mentioned the whole system comprises of multiple boards that are stacked one over the other.  There are 7 such boards and so multiple transceivers, each one with with different number of lines.   In general we are using at configurations of 2,4, 6 & 8 lines each, most of them are unidirectional.  We need these transceivers to support around 1Mbps throughput.  Below is a table of how we use these transceivers in our boards.  Kindly suggest appropriate parts that we can consider.

    Srl. No. Board IC No. of lines Voltage Convertion Currently considered part number Interfaces
    1 1A U9 4 1.8V to 3.3V TXB0104QPWRQ1 GPIO + RS232UART
    2 1A U13 8 1.8V to 3.3V TXB0108DQSR SD Card + RS232 UART
    3 1A U8 8 1.35V TO 1.8V TXB0108DQSR Ethernet MDIO
    4 1B U6 3 1.8V to 3.3V TXB0104QPWRQ1 ADC SPI lines
    5 1C U16 6 1.8V to 3.3V TXB0106PW RS232 UART + RS422 UART
    6 3 U8 4 1.2V TO 3.3V TXB0104QPWRQ1 RS232 UART
    7 3 U9 2 1.2V TO 3.3V TXB0104QPWRQ1 RS422 UART

  • The UART and SPI lines can be handled with TXU devices. (The largest ones have four channels; you might need to combine two chips.)

    MDIO and SD cards use open-drain signals and cannot be handled with the TXB.

    For SD cards, there are specialized translators like the TXS0206(A); you could also use the TXS0104E/TXS0108E.

    For MDC/MDIO, use the TXS0102. Why are the 8 lines for MDIO? (You can use the TXS0108E, if you really have 8 lines.)

  • Thank you so much for your suggestions.  We will modify our circuit accordingly with the suggested parts. 

    The Ethernet lines that we were running short of FPGA banks pins were 


    As I understand these are the optional lines running between Ethernet MAC ( inside the FPGA )  and external PHY.  ( I am new to Ethernet interface )

    Hope we can consider TX0108E for these 8 lines. 



  • Forgot to mention we are using VSC8541XMV-05 PHY from Microchip for this along with Polar Fire / Zynq FPGAs

  • All these ETH_xxx signals except MDIO are unidirectional.

    The TXB has weak outputs and does not work with pull-up or -down resistors.
    The TXS has internal pull-up resistors and does not work with pull-down resistors.
    The TXU works only with unidirectional signals.

    In general, you should use the TXU, when possible. It would also be possible to use the TXS.

  • Thanks a lot for the suggestions.  We are resolved all the Voltage translations on the board as per your suggestions.

    Wanted one more help on the MIPI interface voltage conversation.  We wanted 1.2V to 1.8V and 2.5 to 1.8V level translators for MIPI DSI TX IP on our board which gets connected to an external display. The IP supports ( 1.2 V Low power mode ) and 2.5 V High Speed mode.   As the signals are mostly unidirectional can we consider TXU parts suggested above for this?  Are there any other level converters with supports much more higher speed ?

  • What speed do you need? The fastest level converters are in the AXC family.

  • We are specifically looking for MIPI Level translators. Do you have anything specific for this purpose?

  • Hi Binu,

    For level shifters, the direction / speed / voltage etc are all factors helping to indicate the purpose of translation needed.

    Hence, the  AXC (SN74AXC4T245 / SN74AXC4T774 / SN74AXC8T245) recommendation can support higher data rates (compared to the TXU) for the unidirectional 1.2 V / 2.5 V / 1.8 V MIPI DSI TX signals.

    If up to 240 Mbps for 1.2 V to 3.3 V AXC translation is not sufficient, please help highlight the specific data rate requirement, thanks.

    Best Regards,


  • Thank you so much for your guidance.  It really helped !!