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Original question:

TXB0108: Circuit with two TXB0108 connected in series

TXB0108: TXS0108 and TXB0108 are connected in series..

Yunsoo Jeong
Prodigy 50 points

Part Number: TXB0108

Hi,

I want to connect two types of devices through TTL level UART communication.

Device A interfaces with the internal FPGA via TXS0108.

Through the distribution of the TXS0108's internal pull-up resistance and external pull-down resistance (8.2k), 3.3V is created for interworking with equipment B.

Equipment B uses TXB0108 to shift the 3.3V TX and RX signal levels to 1.8V internal voltage.

When A and B devices are connected by UART, the low signal is unstable, so the two devices cannot communicate or are unstable.

In this case, can TXS0108 and TXS0108 be connected in series and used?

The connection concept is shown in the figure below.

Best regards.

  • 0
    Guru 325360 points

    TXS and TXB translators cannot be connected to each other. (Neither TXS nor TXB outputs have enough drive strength for the other's inputs.)

    And even with the 8.2 kΩ pull-downs, the TXS will sometimes output nearly 5 V because the edge accelerators short the internal pull-ups.

    It might be possible to use the same kind (TXS or TXB) translator on both sides, but a direction-controlled translator would be more robust.

  • 0 in reply to Clemens Ladisch
    Prodigy 50 points

    Thanks

     Both equipments have already been manufactured by each manufacturer, so they can be improved only at the level of pin-to-pin compatible chip change and resistance change.

    In the above situation, is it appropriate to use a TTL to Rs232 converter between the two devices, or change TXB0108 of B device to TXS0108?

  • 0 in reply to Yunsoo Jeong
    TI__Mastermind 47755 points

    Hey Yunsoo,

    You will need to place buffers in between the devices, they are not compatible to be used in series like this.