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TXB0101 noise

NAOKI AOYAMA
Guru 11215 points
Other Parts Discussed in Thread: TXB0101

Hello,

My customer uses TXB0101. He operates it under conditions as follows.

VCCA=1.8V VCCB=3.3V
Connect to external IC by 40ohrm series resistor. Not pulldown or pullup.

So there is a slightly chattering noise in rise edge and fall edge  at Vcc1/2.
The noise occur both from A to B and from B to A. It occur only B port.
He worry about the TXB0101 is miss operation by this noise.

I think the noise is occurred due to impedanse change at Vcc1/2.

Does the series resistor have a bad influence?

  • 0
    TI__Expert 6430 points

    Hi,

    According to your description, the possible reasons are as follows.

    The first reason is that the impedance is changed on port B at VCC/2 as you said.

    The second reason is that the transmission line impedance is mismatch. Could you please check signal integrity when signal is at high voltage level?

    I think that changing resistor value could improve signal integrity. Could you please modify 40Ω to 20Ω and observe the waveform again?

    Thanks

    Lawrence

  • 0 in reply to Wei Lang
    Guru 11215 points

    Hi,

    Thank you for your reply.

    I will try to change resistor value and observe the waveform.

    Thanks,

    Naoki

  • 0 in reply to Wei Lang
    Guru 11215 points

    Hi, Lawrence

    My customer observes the waveform with changing resistor value, 0ohrm, 22 ohrm, 44 ohrm, 51 ohrm.

    The noise remain at B port.

    When he used the resistor 22 ohrm and 44 ohrm, the level of noise is small relatively.

    Should he use a pull-up resistor (over 50k ohrm ) ?

    Regards,

    Naoki Aoyama