• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 2 answers
  • Subscribers 21 subscribers
  • Views 1076 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: VCCa > VCCb

Surendra Malu
Prodigy 40 points
Part Number: TXS0108E
Other Parts Discussed in Thread: TXB0304

Hello,

I am using TXS0108E on one of my designs and in all my stupidity I have used 3.7V for port A and 1.8V for port B, although the datasheet says VCCa <+ VCCb. I am not sure how I read VCCa should be less than VCCb all the time in an exactly opposite way.

That being that, my boards are back and the interfaces on these level translators (I2C, UART) are not working correctly. I am wondering if the choice of voltages is the cause.

Also -

1. Does VCCa have to be less than VCCb for the translator to work or is it just precautionary step?

2. If VCCa must be less than VCCb for TXS0108E to work, then is there any similar, footprint compatible level translator that will work with VCCa >= VCCb?

Thanks,

Surendra

  • 0
    Guru 318050 points

    Biasing Requirements for TXS, TXB, and LSF Auto-Bidirectional Translators says:

    TXS and TXB-type translators require that VCCA is less than or equal to VCCB. This is due to an internal protection diode that can become forward biased when the voltage on VCCA exceeds the voltage on VCCB. When this occurs, large amounts of current flows through VCCA and into the diode, increasing power consumption and potentially damaging the device.

    There is no pin-to-pin replacement with similar electrical characteristics.

  • 0
    TI__Guru 62550 points

    Hi Surendra,

    Unfortunately no P2P in our portfolio which can replace this device given your supply conditions. In the future, it would be good whenever we consider bringing out another device with this supply restriction removed.

    You can consider using TXB0304 which doesnt have this restriction, however, it doesnt work for the I2C interface. 

  • 0 in reply to ShreyasRao
    Prodigy 40 points

    Thank you Clemens and Shreyas for your inputs. Now that I have already designed it the incorrect way and the boards are back, what do you suggest my remedy is?

    Can I keep using the TXS the way it has been hooked up? Will it work? (I can correct the connections in the next revision, but that is not planned out yet)

    In my design, VBAT is 3.7V while VDD_EXT is 1.8V.

  • 0 in reply to Surendra Malu
    Guru 318050 points

    You said in the question that it does not work correctly.

    If you do not want to change the board, you have to flip (dead-bug style) and resolder the chips by hand, or create a daughterboard.

  • 0 in reply to Surendra Malu
    TI__Guru 62550 points

    Surendra,

    I haven't tried this and usually don't recommend but another possibility which might work is to have a current limiting resistor on Vccb supply.

    This will slow the output response/ limit max switching freq. You could try and let us know.