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TXS0108 and I2C

DJH
Intellectual 985 points

It seems fairly straightforward, but is there any reason why a TXS0108 wouldn't work with I2C?  I've got a 2.8V part on one side and a 3.3V part on the other.

Thanks,

-David

  • 0
    TI__Genius 9085 points

    Hi David,


    The TXS0108 should work fine in an open drain application like I2C.

    Are you keeping VCCA ≤ VCCB?

    What behavior are you seeing?

  • 0 in reply to Hattie
    Intellectual 985 points

    Hi Hattie,

    Thanks.  Yes, Vcca is 2.8V and Vccb is 3.3V.  I don't actually have the hardware working too well yet, so I can't debug the I2C yet. 

    Something else that came up though, and that is the state of OE during power up/down.  Do I need to tri-state the TXS0108 during power up/down?  The datasheet just sort of mentions that OE would need to be pulled low in those conditions to keep the high impedance state.  Do I risk damaging the chip or do I just not get reliable performance?  The implication is that a controller will pull OE high during operation; but in my hardware I have it just tied to Vcca.  Do I need to change that?

    Thanks,

    -David

  • 0 in reply to DJH
    TI__Genius 9085 points

    You do not risk damage to the device. The benefit of keeping OE LOW during power-up is that it will prevent any possible glitches from transmitting during this time, however many customers tie OE high without any issues. 

  • 0 in reply to Hattie
    Intellectual 985 points

    Okay, that's all great news.  Thank you so much for following up Hattie, I really appreciate it.

    I'll close this one out as you've answered the only questions I had on the TXS0108.

    -David

  • 0 in reply to DJH
    Prodigy 200 points

    HI,

    I am using TSX0108 translate from 2.5V (A port) to 1.8V (B port). Since I need it power up at low level on B port, I have a 10K ohm resistor pull down on B-port. When I drive A port to high, sometimes works fine, sometimes oscillating. If I change the pull-down resistor to a smaller value, say 511 ohm, B port can’t be drove to full swing. Anyone has seen this problem? Any suggestion?

     Thanks.

  • 0 in reply to Wen73818
    Intellectual 985 points

    Wen,

    Maybe I'm oversimplifying your problem but I couldn't get past the fact that it looks like you have VccA > VccB.  That is just exactly opposite of what the datasheet directs.

    I can't say what will happen to the part if you have VccA at 2.5V and VccB at 1.8V - but it's not going to work correctly.

    Please post your schematic, but I think this is the first thing to check.

    Thanks,

    David

  • 0 in reply to DJH
    Prodigy 200 points

    Thanks. Your are rignt , I have the VccA and VCCB oposite. I'll swithch it. I think it should fix the proble, If still having problem, I'll let you know.