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TXS0108E: Internal pull-ups info

Alberto E.
Intellectual 251 points

Part Number: TXS0108E
Other Parts Discussed in Thread: TXU0304

Hi there!

I'm analyzing the TXS0108ERGY to use in a project that needs level adaptation from 5V to 3,6V. I've seen in the datasheet this device has internal pull-ups in all the lines, connected to their respective supply levels and I have some doubts regarding this features. Is it recommended to use this resistors to set the default states of signals that need a specific value, such as enable pins of another devices? For example, If am driving a RESET signal, that needs a pull-up, can this internal pull-up used instead of placing an external one for time constrained applications?

And... in case I place an external pull-up resistor, the equivalent resistor should be considered to be the parallel between the external resistor and the internal one, depending if the signal is driving high or low (as in section 7.3.5 of datahseet indicates the Rpua and Rpub changes depending if the signal is high or low).

 

And 2... what about if I need to place an external pull-down in a signal? Can this device handle that situation, or do I need another level translator without the internal pull-up to handle that default pull-down pins?

 

Thanks!!

  • 0
    Guru 323430 points

    The internal pull-up resistors are disconnected when OE is low. But when OE is high, the pull-ups can be used as pull-ups.

    The TXS does not work with pull-down resistors.

    What kind of signals? Directions? Frequencies?

  • 0
    TI__Guru 54621 points

    Hi Alberto,

    Thanks for your inquiry. Clemens' comments are applicable and please help to provide more info on use case to help narrow down recommendations. 

    Regards,

    Jack

  • 0 in reply to Clemens Ladisch
    Intellectual 251 points

    Hey! Thank you very much for the answer. In this case, the device is used to convert 5V signals to 3,3V in a CAN Bus IC, so the signals are bidirectional working at a frequency of 500kbps. For now it seems to be fine working with pull-ups but I was wondering if I can use this device wiith other devices that might need pull-down in some lines or whatever. Now it seems to be clear for me, thanks!! 

  • 0 in reply to Alberto E.
    Guru 323430 points

    What signals related to CAN are bidirectional? A typical transceiver's TXD/RXD/STB signals or a typical controller's SPI signals can be handled with the TXU0304.