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TXB0106: Inconsistent output on UART transmission

TISL
Expert 3795 points
Part Number: TXB0106

Dear E2E community,

My customer is facing an inconsistent output signal on our TXB0106.

VCCA=2 to 3V (2x AA batteries)

The SPI is coming from a µp

The UART is coming from a push-pull output

VCCB=3V

The SPI is connected to a flash

The UART is connected to a push pull

The SPI transmission works well.

The UART has got the following behavior (every time), on the pin 11-B5 (CON_TX), when a square signal is applied on pin 6-A5 (BUF_TX)

For information, the power up sequence is:

  • Vcca
  • OE = 0
  • Vccb
  • wait 100ms
  • OE = 1
  • wait 100ms
  • UART signal applied

Schematic used:

Do you have any comments on how to diagnose this issue?

Regards,

  • 0
    TI__Guru 55960 points
    TISL ,

    Is this happening only on single channel everytime and not seen on other channels ? what is the load on B5 ? will it be possible to take scope shot of the incoming signal on A5 ? Is this a low duty cycle signal ?
    Since this is low speed , the TXB should be able to handle this. It seems that the oneshot is being triggered causing it to oscillate. It may be caused due to slow edge rate on the input signal.
  • 0 in reply to ShreyasRao
    Prodigy 20 points
    Hello Shreyas,

    Thank you for your quick answer!
    Regarding the rising edge, it takes about 13ns.

    After further testing it seems that with nothing on the output, and with a better probe (3pF), we have the expected (correct) results. But as soon as we use anything else such as a 11pF probe we get what you see in the original post.

    TD
  • 0 in reply to Alex Sorita
    TI__Guru 55960 points
    TD ,
    Very interesting observation and gives some clue that it is being affected by capacitive loading on the outputs.
    Please refer to 8.3.6 of the TXB0106 datasheet about the max cap loading it can operate within.