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TXB0108: Can't run TXB0108

Ivan Rock
Intellectual 775 points
Part Number: TXB0108

Hi,

I got my TXB0108 board, it has everything to plug and go. I wanna use it for SPI, to communicate between Arduino Mega, which has 5 v level and nrf51 which has 3.3v level.

So, I used 4 channels. Vcca connected to 3.3v, Vccb connected to 5v. GROUND is common.

Channels 1 to 4 of A side connected to MOSI, MISO, CLK, CS of nrf51, Channels 1 to 4 of B side connected to MOSI, MISO, CLK, CS of Arduino. OE connected to Vcca, other 4 pins of sides A and B are floating and are not connected to anything. I run my program and logic analyzer shows incorriect data, usually that I send FF and receive FF, of course I send another data.

Once when I just got this chip, I could connect sides incorrectly. 5v to side A, 3.3v to side B, also OE to 5v. Could I damage this chip with this configuration? Datasheet says that Vcca <= Vccb, but if Vcca > Vccb it doesn't damage the board. However, Vcca power supply must be up to 3.6v

  • 0
    TI__Guru 56100 points
    Hi Ivan,

    The Vcca <=Vccb is a datasheet recommended condition. There is a diode path existing between Vcca and Vccb which will be biased if there is a violation(Vcca>Vccb).
    Also, do not leave the A/B ports floating as they are CMOS inputs which can float to values causing excessive Icc current.
    what do you mean by incorrect data?
  • 0 in reply to ShreyasRao
    Guru 244220 points

    Also, do not leave the A/B ports floating as they are CMOS inputs which can float

    The TXB I/Os are also connected to the output buffers (it's the equivalent of a bus-hold circuit) and cannot float.

  • 0 in reply to ShreyasRao
    Intellectual 775 points

    I mean when I send data like 0x20, 0x00, 0x00 via SPI from mcu A (it's connected to side A of TXB) and listening data on side B, also I connected Logic analyzer on this side, my analyzer shows that mcu A sent 0xff, 0xff, 0xff.

    Maybe it's because my other 4 channels ain't connected and have floating state?

  • 0 in reply to Ivan Rock
    Guru 244220 points
    What do you actually see with the logic analyzer? Show the waveforms. Do you have an oscilloscope?

    Does it work without the logic analyzer?