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TXB0104

Christian Pedersen
Prodigy 120 points
Other Parts Discussed in Thread: TXB0104

Hi

Im using a TXB0104 for level translating on a debug port, A side is 1,8V and B side is 3,3V. OE is always connected to 1,8V for enable.

I dont have any pullup or pull down resistors on A or B side. Baud is 115 Kbps.

The problem is: I only get garbage on my terminal connected on the B side. When i connect a 1nF capacitor to A1 witch is TX from CPU to port A then

everything works perfectly, why does this happen ?

Signals on A1 is high in not used state and witout capacitor, when signals starte to flow i only get garbage on the terminal. drive strengt from CPU is set to high.

BR

Christian

  • 0
    Mastermind 7395 points

    I undestand that you have unused I/O pins. Pins that are unused must be tied at both sides to the same level. For example, you can connect both sides of an unused port to GND.

    See the note:

    (1) The A and B sides of an unused data I/O pair must be held in the same state, i.e., both at VCCI or both at GND.

  • 0 in reply to Avi Chami1
    Prodigy 120 points

    Hi

    No i dont have unused pins, pins are used for Rx, Tx, Cts, Rts.

    I think the solution is to use TXS0104 instead, but why the device works with 2nF at the A1 input is strange ? do you have an explanation for that ?

    BR

    Christian

  • 0 in reply to Christian Pedersen
    Mastermind 7395 points

    Even if you connected CTS and RTS to the buffer, are they connected at the cable? These days nobody uses CTS and RTS,... so they could be floating.

    The other explanation is that your signals are catching too much noise from somewhere. Since the TXB decides direction upon signal activity, a noisy signal could force him to change direction... The capacitor kills the noises and the unwanted directions changes stop. Maybe.

  • 0 in reply to Avi Chami1
    TI__Expert 4705 points

    Hi, Christian

    Yes, I have the same thoughts with Albert.

    Acutally, if the signals are push pull , TXB0104 should be OK, but if the signals are open drian, only TXS010X can work.

    If you still have the same issue after you confirm your input signals are OK, please let me know below information for my better understanding your issue.

    1. Please share with me your shcematic or diagram 

    2. All your B side are garbage? all B1 to B4? could you share with me the waveform of them?

    3. Have you measured the A1 to A4, could you share with the the waveform of them?

    4. I am not very clear for what you said "when signals starte to flow i only get garbage on the terminal. drive strengt from CPU is set to high."  could you please clarify it for me?

    One applicaiton note for TXB family for your reference.

    http://www.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=scea043

    BR
    junjie