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TXS0104E: glitch in the rising edge of the B port

Lacey Lin
Intellectual 2900 points
Part Number: TXS0104E

Hi Team,

My customer use the TXS0104 to translate the voltage for the I2C signal. And they found there is a glitch in rising edge of the SDA signal tested in the B port.(show as below).

Below is the schematic:

1. I have asked them to remove the 2.2K and 4.7K pull up resister, but it seems no help.（see below）

2. In the B port, they also connect the 100pf cap to ground in the SDA and SCL, after they disconnect the 100pf resister, the issue seems to be fixed.

1. Does the 100pf cap cause the issue? If not, what may be the cause?

2. If the 100pf cap can cause the issue, do you have some recommend method to optimal the B port signal?

Lacey

Thanks a lot!

  • 0
    TI__Guru* 96862 points
    Hi Lacey,
    I have asked our translation expert to take a look. He should be back with you tomorrow.
  • 0
    TI__Guru 58490 points
    Lacey,

    will take a look at this tomorrow and reply.
  • 0
    TI__Guru 58490 points
    1) The external pullup resistors must be removed, they form a parallel resistor combination with the 10k resistor within the TXS device.
    Please refer to the app note :
    Effects of pullup pulldown resistors on TXS device here :
    www.ti.com/.../scea054a.pdf

    2) The input signal is slow and is currently violating the input transient spec as well which is 10ns/V. The input signal must be faster than what currently is. The TXS is a passive switch passing through the low level signal as it is. Please remove the 100pF loading on the B port.
    The oneshot is being triggered however, the loading on the B port is high enough to not reach the final level and the 10k resistor has a slow response to take the signal to the final value.
  • 0 in reply to ShreyasRao
    TI__Intellectual 2900 points
    Hi ShreyasRao,
    Thanks for your reply!
    1.your recommendation is to remove the 2.2K and 4.7K resistor and to remove the 100pf cap
    2. the B port cap will result the signal not reach the final level and cause the glitch because of the one shot function? Is it right?
    3. According to customer's test, it seems the low input transient can't cause the issue. When they remove the cap, the rising time is about 800ns and the signal don't have glitch.

    Lacey
    Thanks a lot!
  • 0 in reply to Lacey Lin
    TI__Guru 58490 points
    2) Signal not reaching the final value is because of the cap loading causing the one shot function to time out midway causing the non-monotonic behaviour of the signal.