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TXB0104PWR OE resistor value

Edmond Chiu
Prodigy 170 points
Other Parts Discussed in Thread: TXB0104

In the datasheet of this part, it states that 

"When the output-enable (OE) input is low, all outputs are placed in the high-impedance state. To ensure the
high-impedance state during power up or power down, OE should be tied to GND through a pulldown resistor;
the minimum value of the resistor is determined by the current-sourcing capability of the driver.
The TXB0104 is designed so that the OE input circuit is supplied by VCCA."

I am currently have VCCA using 3.3V. What is the recommended value for the minimum value of the resistor? Thanks.

  • 0
    Prodigy 170 points

    Alternate set up question: I have followed what was said in http://e2e.ti.com/support/interface/etc_interface/f/391/t/305156.aspx and instead tied my VCCB to OE without a resistor. I now have VCCA at 3.3V and VCCB/OE at 5V. I am now running a test in which I will convert 2 3.3V SPI writes to 2 5V SPI writes. Here are the photos of both signals: (NOTE: I currently have the system clock at 8Mhz and the SPI clock at 2Mhz. The microprocessor is a PIC18F26K80)

    http://imgur.com/rNJb6vh <- signal before level shifting

    http://imgur.com/7uTTzGC <- signal after level shifting

    I am noticing also that the signal is 4V and not 5V. Are there any recommendations I should take to fix this signal?

    I also have chip selects (3.3V) that I am trying to level shift and occasionally, the reading would be 2.4V and other times, it would be 5V. Is there any reason why this is? Thank you.

  • 0 in reply to Edmond Chiu
    TI__Expert 6430 points

    Hi,

    I think 10k pull up resistor is fine.

    I can open the signal photoes, could you upload again?

    Thanks

  • 0 in reply to Wei Lang
    Prodigy 170 points

    Here are my reuploaded pictures:

    http://postimg.org/image/3o8wd4vzl/9892bbb9/ (this image is before the level shifting)

    http://postimg.org/image/xv7ycurnj/cdfe3a21/ (this image is after the level shifting)

    So what you are suggesting is to put a 10k resistor connected on one end to the OE pin and the other end to a 5V power?

    EDIT: I have tried the 10k pull up resistor and I have almost the identical image after level shifting above. Is it possible that it has nothing to do with the OE pin but the frequency?

  • 0 in reply to Edmond Chiu
    TI__Expert 6430 points

    Could you add them as attachment or email to me since I still cannot be access to webpage. My email is langwei@ti.com.

    Thanks