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TXB0108: TXB0108 - Open drain pin support

Jeeveth Komaravel
Prodigy 50 points
Part Number: TXB0108


Tool/software:

Hi Team,

We are using TXB0108 in our design. We have connected open drain pin in this level translator with the pullup of 2.2K. Functionality side we are not facing any issue. It is working fine. But in datasheet, it is mentioned as that this level translator will not support open drain and also pull value should be more than 50K. Is there any possibility of receiving failure in future with this level translator if we connected open drain pin in this level translator with the pullup of 2.2K. Kindy clarify. 

  • 0
    TI__Mastermind 43761 points

    Hi Jeeveth,

    TXB is not designed for open drain drivers due to its weak push-pull drivers. For open drain level shifting, the TXS-Type translators should be used instead (note that this device includes internal pull-ups so the external 2.2kohms can be removed additionally). 

    Regards,

    Jack 

  • 0 in reply to Jack Guan
    Prodigy 50 points

    Hi Jack,

    We are implemented the design based on the TXB for open drain. From the funcionality wise, we are not facing any issue. Will it create any issue for TXB IC.

    Without external Pullup, the line is not going to high. That's why we have added external pullup. 

    Thanks,

    Jeeveth K

  • 0 in reply to Jeeveth Komaravel
    TI__Mastermind 43761 points

    Hi Jeeveth,

    No concerns for TXB IC. It is more so compatibility concerns with the open drain I/Os that the TXB is interfacing with, as the device was not intended to be used for open-drain applications. 

    The reason  for >50kohms pullups suggestion is to avoid the VOL levels from being heightened due to internal 4k series resistance, as seen in https://www.ti.com/lit/an/scea054a/scea054a.pdf?ts=1744735358188.

    Regards,

    Jack

  • 0 in reply to Jack Guan
    Prodigy 50 points

    Hi Jack,

    As per the SCEA054A document, testing was done from A to B configuration. In the A to B configuration, 4K series resistor in B side. That why we facing VOH and VOL issue. 

    But in our case, we are using B to A configuration. As per block diagram, in the configuration 4K series resistor in A side. As per our understanding, Voh and Vol issues will come if we put pull up/pull down in A side. We are putting pullup in B side for open drain. Will it create any issue? 

    Thanks,

    Jeeveth

  • 0 in reply to Jeeveth Komaravel
    TI__Mastermind 43761 points

    Hi Jeeveth,

    The internal 4kohm resistors exists on A and B side and open drain drivers needs pullups on both sides of the translator to interface properly. To reduce complications and ensure compatibility, this is why TXS is strongly suggested over the TXB for open drain level shifting applications. 

    Regards,

    Jack