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TXB0104-Q1: OE pin is pulled up VCCA

Tomoaki Yoshida91
Genius 5255 points
Part Number: TXB0104-Q1

Hi Team,

We will pull up OE pin to VCCA, because I/O is always active in our system.

I have some questions for above usage.

#1

Please tell me recommended pull up resister tied to VCCA.

#2

In our usage, OE may be High and I/Os are active before VCCB rise up.

In this case, will the device have problems?

I think that Bx is high impedance, but what is the state of Ax?

I assume that Ax is not active pulled up or pulled down externally.

Best refards,

Tomoaki Yoshida

  • 0
    TI__Guru* 97046 points
    Hello Yoshida-san,
    If the I/O's of the TXB are always turned on (ie you are not using the OE pin) then no pull-up resistor is required. Just connect the OE pin directly to VccA.

    As described in section 11 of the datasheet, Power Supply Recommendations, "VCCA ≥ VCCB does not damage the device, so any power supply can be ramped up first"

    What is the state of VccB? If it is 0V, then all I/O pins will be in a high-impedance state.
  • 0 in reply to Emrys Maier
    Genius 5255 points
    Hi Emrys-san,

    Thank you for your support.

    I understand that OE pin can be directly connected toVCCA.

    You said that "VCCA ≥ VCCB does not damage the device, so any power supply can be ramped up first".
    However, VCCA ≤ VCCB is also written in the datasheet.
    Even when connecting OE directly to VCCA, is there no damage at power on?
    I assume that there are all cases of VCCB from 0 V to 3.3 V and VCCA is 3.3V.
    For example, if VCCA and OE are 3.3 V and VCCB is 1.8 V in the middle of the rise, VCCA <VCCB may be violated because all the drivers are active.
    I am worried that such problems may arise if OE is connected directly to VCCA.

    Best regards,
    Tomoaki Yoshida
  • 0 in reply to Tomoaki Yoshida91
    TI__Guru* 97046 points

    Hi Yoshida-san,

    You left off the important condition of that statement:

    During operation, ensure that VCCA ≤ VCCB at all times.

    During power-up sequencing, VCCA ≥ VCCB does not damage the device, so any power supply can be ramped up first.

    The device will not be damaged by VCCA > VCCB, however the device may not operate as expected while this is true.

  • 0 in reply to Emrys Maier
    Genius 5255 points

    Hi Emrys-san,

    Thank you for your support.

    I think that connecting the OE directly to the VCCA causes the following cases, which may be During operation.

    Although we use VCCA and VCCB are the same 3.3 V, they are supplied from another power supply.

    When VCCA first reached 3.3 V and VCCB is delayed and still 1.8V.

    I assume that It is input A1 to A4 at this time.

    In this case, dose it meet During operation and VCCA> VCCB?

    I think that it should be ok,  if this case is considered to be in the power up sequence.

    Please tell me your opinion.

    Best regards,

    Tomoaki Yoshida

  • 0 in reply to Tomoaki Yoshida91
    TI__Guru* 97046 points
    Hi Yoshida-san,
    Are you saying that the device is transmitting data before VCCA = VCCB?
  • 0 in reply to Emrys Maier
    Genius 5255 points
    Hi Emrys-san,

    Thank you for your reply.

    Yes.
    I meant that data transmitting was started before VCCB reached VCCA.

    Best regards,
    Tomoaki Yoshida
  • 0 in reply to Tomoaki Yoshida91
    TI__Guru* 97046 points
    I would recommend delaying data transmission until the supplies meet the condition VCCA ≤ VCCB, otherwise, I cannot guarantee that the device will operate correctly.