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TXS0206: About TXS0206 output ringing

Vera Mao
Expert 5065 points
Part Number: TXS0206
Other Parts Discussed in Thread: OMAPL138, ,

hi dear supporting team,

customer is using flying wire to connect from their brd to our TXS0206 EVK, connect with OMAPL138. and meet below issue:

1. if VCCA goes up ealier than VCCB, there will be ringing happens as below plot, when powering up, OMAPL138 is also in reset status.

2. if VCCB goes up earlier than VCCA, then everything is normal.

3. in nromal operation, if reset OMAPL138, there will be same issue happens. 

the sch is as below, they did not include the serial 24Ohm resistors in it. EN is connected to VCCA.  if powering up TXS0206 and then provide EN, then everything is ok.

so double check with you:

1. if EN direct connect to VCCA, is there any power up sequence requirement?

2. what's the root cause of such issue? is it due to the bug of the chip?  anyway to avoid?

tks a lot!

  • 0
    TI__Guru* 96591 points
    Hi Vera,
    I have asked Shreyas to look into this. He should be back with you soon.
  • 0 in reply to Emrys Maier
    TI__Guru 55990 points
    Vera ,

    24 ohm series resistor can be removed. Are the CLKA/ Clk-f left open ? please have defined levels on them.
    what is the probe capacitance and where is the measurement done ?
    There is no restriction i see on the datasheet with the power sequencing or the Vcca or Vccb to be powered up first.
    Is there a possibility of trying a different device and comparing the performance ?
    can powering up Vccb first which doesnt have ringing be done for your application ?
    There is no known bug as i know, with the device released 8 years ago.
  • 0 in reply to ShreyasRao
    TI__Guru 55990 points
    Vera ,

    also , i would suggest using the TXS0206A device to compare the results.
  • 0 in reply to ShreyasRao
    TI__Expert 5065 points

    hi SheryasRao,

    thank you very much for the reply!

    what's the difference btw 0206A and 0206?

    customer only test one pcs on our evk,  the cap of the probe is 3.9pF, and test point is at the needle plug on the demo, in actual application, they could not guarantee VCCB first, while they could delay the enable pin. 

    they tried remove the serial resistors, while there is also oscillation shows up.  do you think it is related with the probe? 

    CLK-F is open, CLKA is connect with OMAPL138, when powering up, OMAPL138 CLK will be in high impedance status,  in such application, do they need add pull up resistor at CLK? 

    TKS a lot!  

  • 0 in reply to Vera Mao
    TI__Guru 55990 points
    Vera ,

    With such low cap values , i dont think its related to the probe.
    Please have defined values at the Clk pins.

    I do not have the background on what were the changes on TXS0206A , however , i will suggest to try that device as replacement. The A indicates die revision.
    Serial resistors is not needed as it will create voltage divider but not necessarily have the oscillations disappear.
  • 0 in reply to ShreyasRao
    TI__Expert 5065 points
    Hi Shreyas,
    customer add 10K pull up or pull down resistor at CLK-F, and will get the same phenomenon. while if add 300pF at CLKB , it will solve the issue.
    I checked my apply history, the brd customer got is already 0206A. could you help double check on your evk to see whether it is what it is? tks a lot!
  • 0 in reply to Vera Mao
    TI__Guru 55990 points
    Vera ,

    although , i wouldnt suggest having the cap on the clk lines, can the customer not use them if it doesnt have the ringing?
    i also notice that there is no bypass caps on the power lines, is it true ? can they add additional caps (0.1uF ) close to the device Vcc pins to see if that helps ?
  • 0 in reply to ShreyasRao
    TI__Expert 5065 points

    hi Shreyas,

    do you concern about the Tr/Tf after adding the cap at CLK? customer only use 1M speed, and found the Tr/Tf still be ok.

    as for power supply decoupling cap, there is already one one the evk for each supply, customer add additonal 0.1uF, while no progress.  

    do you think it is what it is , or there may be some bug on the evk they got? tks!

  • 0 in reply to Vera Mao
    TI__Guru 55990 points
    The other debugging to try would be to replace the existing devices with another set of devices.
    if not , I would recommend to power up with Vccb first and then Vcca which can be software controlled