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TXB0104: TXB0104 Oscillation

Mason Noh
Expert 2490 points
Part Number: TXB0104
Other Parts Discussed in Thread: TXB0102,

Hi TI team, 

i am using TXB0104 for shifting SPI signal of 3.3V to 1.8V.

But some boards has oscillation of I/O. and we improved by adding capacitor(820pF) between A2 and GND.

Please let me know root cause and side-effect.

Thank you.

  • 0
    TI__Guru 59160 points

    Hi Mason ,

    I would suggest you to consider replacing this with the 2 channel version TXB0102 since there are unused channels on the 4 channel TXB0104.

    Just curious if the signals are SPI or UART since TX and RX are part of UART interface. what is the datarate or the speed? I assume it is very slow going by the time scale on the scopeshot.

    Section 8.3.5 on the datasheet mentions that the output loading on the TXB0104 can be up to 70pF. So, I would not suggest having 800pF loading. 

    Since the timescale is large(100ms?) the rise / fall time will be affected with such large output cap which may also affect the devices downstream.

    What is the input signal into the TXB look like and does it satisfy the input transition rate requirement as mentioned in the ROC? I see that the Vcc supplies have bypass caps, but is there scopeshot of the supply when the oscillation occurs? I would suggest to add a small series resistors about 16-50ohm to have a impedance matching which may remove the oscillation. 

  • 0 in reply to ShreyasRao
    TI__Guru 59160 points
    Hi Mason,

    Please let me know if you have additional details. If not, I will close the thread.