• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 20 subscribers
  • Views 1126 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TXS0108E: Signal is not converted without distortion

Krunal Zala
Prodigy 120 points
Part Number: TXS0108E
Other Parts Discussed in Thread: SN74AXC4T774

Hello,

I have a TXS0108E for converting logic from/to 1.8V & 3.3V.

Please see below interface details.

I need help to resolve following issues:

  1. The SCK signal as soon as connected to CODEC side, the clock gets severely distorted. Not sure why?
  2. What I noticed is, if SCK signal from TXS is not connected to CODEC then SCK(at 3.3V side) does not have severe distortion. I suspect that the CODEC I am using has active pull-up on SCK(another other signals) and due to which TXS is misreading about which end is driving?
  3. In fact, I read the TXS0108E datasheet but could not find information showing how direction of the signal is automatically chosen?

Request you to help me resolve this interfacing issue.

Regards,

Krunal

  • 0
    TI__Genius 16735 points

    Hi Krunal,

    Based on your schematic, it seems like all your signals are unidirectional. If that is the case, I think you might be better off using a device like SN74AXC4T774.

    Does the codec SCK line require a high drive strength? Are you using long transmission lines?

    Here is an appnote on how to use our TXS devices and how they work:

    http://www.ti.com/lit/an/scea044/scea044.pdf

    Thanks!

    -Karan

  • 0 in reply to Karan Kotadia
    Prodigy 120 points

    Hello Karan,

    Well, my current product selects the direction of the signal during initialization and once I2S is initialized(i.e. who is master and slave) the direction will remain same until next POR happens.

    >>Does the codec SCK line require a high drive strength?

    I will find out but you can let me know how much sink/source current TXS0108E?

    >>Are you using long transmission lines?

    The interface length is approximately 10-12 inches.

    Therefore, I request you to help me understand how to tackle signal disturbance issue while using  TXS0108E

    Regards,

    K Zala

  • 0 in reply to Krunal Zala
    TI__Genius 16735 points

    Hi,

    Is your application open drain? If so the clock speed might be too much for the device to handle.

    As you can see in the FAQ about our auto bidirectional translators, TXS devices have no drive strength. This is why a long transmission line of 10-12 inches will trigger the one shots multiple times due to the reflections in the line.

    PCB signal trace-lengths must be kept short enough so that the round-trip delay of any reflection is less than the one shot duration, approximately 30 ns, ensuring that any reflection encounters low impedance at the source driver.

    The best device for such long transmission lines will be SN74AXC4T774. It has 4 individual direction pins to choose the direction of the device. So maybe at POR, you could use a GPIO or some logic to configure the direction of the channels.

    Thanks!

    -Karan