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TXS0104E: the TXS0104 driver current

huquan huang
Prodigy 50 points
Part Number: TXS0104E
Other Parts Discussed in Thread: SN74LVC2G66, SN74AHC4066

MCU (MCU_3.3V)---uart----TXS0104E---uart---FPGA(FPGA_3.3V);  IN  my system , i'm use the TXS0104E to isolate UArt signal .  the  mcu_3.3V rise first ,and long time later then  fpga_3.3V rise. but i'm make a mistake, the TXS0104E OE/ pin is connect to the  mcu_3.3V  direct and  there is no resistance to gnd.  I want to known, in mine system, the fpga uart pin will be damage or not ?

the mcu chip STM32L431CB  ,the FPGA chip  XC7Z007S

  • 0
    Guru 271790 points

    The TXS is a level shifter, and does not isolate anything (for low signals, there exists a direct connection through the chip).

    The datasheet says:

    To ensure the high-impedance state of the outputs during power up or power down, the OE input pin must be tied to GND through a pulldown resistor and must not be enabled until VCCA and VCCB are fully ramped and stable.

    So in your circuit, the I/Os on the FPGA side are not in the high-impedance state, and can apply 3.3 V to the FPGA pins.

    To disconnect those UART signals, better use an analog switch (e.g., SN74LVC2G66 or SN74AHC4066).