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TXB0104: TXB0104YZTR issue case

Part Number: TXB0104

Dear TI :

We found the issue,when UART signal is connected around 1.5m cable that after TXB0104YZTR level shifter will has about 45MHz oscillate waveform(as below picture)

Could you help to check if this waveform is capacitive loads > 70pF phenomenon mentioned in the TXB guideline?

Do you have any suitable solution to resolve this issue?

thanks.


 

 

  • The capacitance of the 1.5 m cable is likely to be much higher than 70 pF.

    UART signals are unidirectional, so it is possible to use a direction-controlled voltage translator with proper output buffers.

  • Hi 

    If won’t expect to have PCB layout changes, prefer to study TXS0104 solution.

    With capacitive loading >70pF, the TXS-type devices will still successfully operate at lower data rates. mentioned in the TXS guideline.

    I have some question as below,please help to check , thanks.

    1.What is the rated load capacitance of the TXS0104 ?

    2.If capacitive loading > 70pF ,Does UART data rate can be TXS0104  surpport?

  • You got oscillations because the parasitic capacitances and inductances in your circuit created ringing with an amplitude that is high enough to trigger the edge-rate accelerators.

    The TXS also has edge-rate accelerators.

  • Hi Clemens :

    is TXB internal weak buffer with circuit capacitances and inductances to produce oscillation or edge-rate accelerators?

    I have tried to rework TXB0104 change to TXS0104 then oscillation issue is resolved

    so want to double check TXS0104 is workable for capacitive loading >70pF design? thanks.

  • The TXB has edge accelerators for both rising and falling edges.

    The TXS has edge accelerators only for rising edges, and a low-level signal is driven with a lower impedance, so it would be expected to be more robust than the TXB.

    Can you check with the oscilloscope whether the TXS has any ringing?