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Using TXS0102 for I2C translation 1.8v to 5v

Peter Thompson85
Prodigy 70 points
Other Parts Discussed in Thread: TXS0102, LSF0102

I am connecting an IGEPv2 (Beagleboard clone) I2C output to Microchip AR1021 for a touch panel.    I know the I2C port works as I can connect Freescale FXOS8700 (no translator needed as it uses 1.8v) and find it with i2cdetect. 

When I introduce the TXS0102 translator to convert 1.8v to 5v for the AR1021, I2C does not work.  I am using pins A1 to B1 for SCL and A2 to B2 for SDA on the TXS0102.   Using the oscilloscope,   my SDA signal is translates  ok, but the SCL signal is being somehow corrupted on the 1.8v side so the 5v signal, while translated, is wrong. 

I have no pullups on A1, A2 and 4.7k pullups on B1, B2.   This is my second time trying to use TXS0102 for I2C translation with no luck.

Any suggestions?

  • 0
    TI__Guru 55980 points
    Hi Peter ,

    Welcome to e2e .
    The TXS devices have built in 10K pullups in them and I believe having 4.7K pullups on B1 B2 are unnecessary unless you have a reason for them. I have the applications support copied for additional support . If you can send in the schematics , would be helpful .
    wanted to know if you had considered LSF0102 for the application ?This would need the external pullups for up translation and for I2C would require pullups on the A side as well.
  • 0
    TI__Expert 6335 points
    Peter,

    An oscilloscope waveform capture would go a long way in helping us to debug your system. Thanks.

    Best Regards,
    Nirav
  • 0 in reply to ShreyasRao
    Prodigy 70 points

    TXS0102expander.pdf

    AR1021expander.pdf

    ShreyasRao said:
    Hi Peter ,

    Welcome to e2e .
    The TXS devices have built in 10K pullups in them and I believe having 4.7K pullups on B1 B2 are unnecessary unless you have a reason for them. I have the applications support copied for additional support . If you can send in the schematics , would be helpful .
    wanted to know if you had considered LSF0102for the application ?This would need the external pullups for up translation and for I2C would require pullups on the A side as well.

    ShreyasRao said:
    Hi Peter ,

    Welcome to e2e .
    The TXS devices have built in 10K pullups in them and I believe having 4.7K pullups on B1 B2 are unnecessary unless you have a reason for them. I have the applications support copied for additional support . If you can send in the schematics , would be helpful .
    wanted to know if you had considered LSF0102for the application ?This would need the external pullups for up translation and for I2C would require pullups on the A side as well.

    AR1021try2schematic.pdf

    My apologies!    I was using the email reply and it was not being posted.   I built a simple TXS0102 expander board and a AR1021 expander board and got it working.    I removed the pullup resistors and other resistors which must have caused the problem.  

    For completeness, ttached is the schematic causing the problem plus the oscilloscope captures for scl both 1.8v and 5v (the sda signal seems ok)  when I send i2cdetect -r 2 to the device

    Also attached is the expander board (which worked)