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Original question:

TXB0104: relation of VCCA and VCCB

TXB0104: TXB0108 - Consequences of violating requirement VCCA <= VCCB

Jeff Richelsoph
Prodigy 90 points
Part Number: TXB0104
Other Parts Discussed in Thread: TXS0108E, TXB0108,

Hello.  We are debugging a design that uses the TXB0108.  The part does not work in our application because of pull-ups internal to the part attached to the TXB0108.  We solved the issue by using the TXS0108E and the interface is operational.  However, a separate issue exists -  VCCA=3.3V and VCCB=2.5V which violates the requirement that VCCA <= VCCB.  The related question for the TXB0104 references internal diodes not shown on the block diagram. What are the consequences of this violation over industrial temperature and time?

Thank you

  • 0
    Guru 316780 points

    VCCA and VCCB Bias Requirements for Bidirectional Translators (SCEA060) says:

    TXS and TXB-type translators require that VCCA is less than or equal to VCCB. This is due to an internal protection diode that can become forward biased when the voltage on VCCA exceeds the voltage on VCCB. […] VCCB fixed at 2.5 V and VCCA swept from 2.5 V to 3.5 V:

    As shown in Figure 4, … when the voltage on VCCA exceeds the voltage on VCCB by roughly 0.6 V, the diode begins to conduct and the ICCA current begins to drastically increase as VCCA increases.