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TXS0108E: Oscillation on RESET pin

Brian Antheunisse
Expert 5305 points
Part Number: TXS0108E

Hey guys,

I am observing a very strange issue. Reset pin of TXS0108E has a 1K pull-down. When pull down is connected I see attached waveform. When I remove pull-down pin is pulled high to 1.8V. 

Is this issue due to autosense? The same IC is used on a different evaluation board I used to configure LMK clocking chip. I see something similar issue, only thing I do not see oscillation but levels are not right on pin with pull down (RESET/SDO).

  • 0
    TI__Guru 62100 points
    Hi Brian,

    Please share the full schematic of the TXS0108e, and the associated IO channels connection.
    is it directly connected to Vcca without any series resistors? what is the waveform on the Vcca pin?
    Would 1K pulldown is necessary for the operation?
  • 0 in reply to ShreyasRao
    TI__Expert 5305 points
    Shreyas,

    I am sending you schematic internally. LMK SDO pin is multiplexed with RESET. The RESET signal is active HIGH, hence there is a pull down.
    Now after power up LMK configured as 4 pin interface when SDO pin becomes output pin. This creates lots of issues.

    I am thinking to replace all these with unidirectional or bidirectional with directional control instead of autosense. However, before doing that I thought to check with you why I am observing strange behavior.
    Even on TI evaluation board, U6.1, if you add 1K pull down you can observe the waveform I shared. I guess this is due to autosense, as level translator has 10K internal pull-up and external 1K pull down, not sure??

    Thanks,
    Brian
  • 0 in reply to Brian Antheunisse
    TI__Guru 62100 points
    Hi Brian,

    We advise to not have any external pulldown or pullup on the TXS IO channels.
    Read the app note:
    www.ti.com/.../scea054a.pdf
    but this should not be the cause of reset pin oscillation.
    will take offline.