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I2C interface through TXS0104E

riyaz mohammed
Prodigy 10 points
Other Parts Discussed in Thread: OMAP3530, TVP5150AM1, TXS0104E

Hi,

We are TXS0104E buffer for I2C interface signal's voltage level translation. Here our I2C host is OMAP3530 which is 1.8V signal level and device is TVP5150AM1 which is3.3V signal level. So we are using TXS0104E for voltage translation. 

When we try to access the TVP5150AM1 from OMAP3530, we are not able to get the acknowledgement. Whille probing the signals we got the waveform as shown below. Please let us know your comment on this. Here it looks like TVP5150AM1 is not able to pull low the 9th bit (acknowledgement) fully.

 

I2C Waveform in 3.3V device side (After TXS0104 buffer):

 

I2C Waveform in 1.8V device side (BeforeTXS0104 buffer):

 

Regards,

Riyaz

  • 0
    TI__Genius 9085 points

    It looks like the signal isn't going low even before the TXS0104. I couldn't find the maximum drive strength for the TVP5150AM1. But what may be happening is that it is not pulling enough current through the pull-up resistors to bring the bus to a lower voltage. It also looks like there is a lot of current going through the TXS device. This will raise the VOL level because the TXS has some RON. 

     

    Do you have any external pull-up resistors? Any series resistors on the line? Are the OMAP internal pull-ups disabled?

    Are all the GNDs connected?

  • 0 in reply to Hattie
    Prodigy 130 points

    Yes, we have pullup resistors on both the side. On TVP5150AM1 side, we have 1.2K pull up and OMAP side we have 4.7K pull up. Regarding series resistor,we don't provide any on these lines. Also all GND pins are connected in TCP5150Am1,TXS0104E and OMAP.

  • 0 in reply to Pradap Raj
    TI__Genius 9085 points

    Since the TXS has internal pull-ups, you don't need external pull-ups. External pull-ups will actually increase the amount of drive strength required by the driver and increase the current through the TXS.  

    Try removing these.

  • 0 in reply to Hattie
    Prodigy 130 points

    We tried by removing pullup on both sides and getting the same result. What else we can try to solve this?

  • 0 in reply to Pradap Raj
    Prodigy 20 points

    I had similar problem and found a cause for my case.

    When both port (A and B) were driven by other devices, this kind of waveform is observed.

    Please check possible driver devices and their output enable control logic.