This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TXB0101: Input Voltage Specification

Part Number: TXB0101
Other Parts Discussed in Thread: SN74AUP1T157, SN74AVC4T245, , TXB0104

Regaridng the High/Low Level Input Voltage on the Recommended Operating Conditions, the value is VCCI/0V respectively.

If the Undershoot is observed and the voltage on the input is negative, can we use the input voltage on the Absolute Maximum Ratings which is -0.5V - 6.5V to judge the undershoot is not an issue for  the reliability or long term functionality of the device, or not?

And could the above logic be applied to other TI's logic device which has the input clamp diode?

*For example, SN74AVC4T245, SN74AUP1T157.

Thank you.

  • The absolute maximum ratings allow lower voltages as long as the current is limited. As long as you stay inside those ratings, there will be no permanent damage.

    The TXB (and AVC/AUP etc. families) has a clamp diode from GND to the I/O pin. For voltages between 0 V and about −0.5 V, only a small leakage current flows. For voltages below −0.5 V, the diode is forward biased and a noticeable current flows, but that current still depends on the voltage. The datasheet does not specify the characteristics of the diodes, but for certain voltages, the current is still below the absolute maximum rating of 50 mA, and safe.

    The TXB0101 has no IBIS model, but the TXB0104's model says that the worst-case current stays below 50 mA down to about −0.95 V.

    Do you actually observe undershoots? Due to the bidirectional design, the TXB's I/O pins have a relatively low impedance of about 4 kΩ.

  • Dear Ladisch-san,

    Thank you for you quick reply.

    No, I have not observed undershoots.  I am going to validate the input voltage on our product.

    But I think that when we measure voltage on the input pin, it could be negative voltage because of noises.

    So, I would like to check if the negative voltage is an issue.

    I understood that for devices which have a clamp diode,  it will be no permanent damage for 0V to -0.5V, because the current is smaller than the Inpu clamp current.

    Just making sure, for 0V to -0.5V, it will be no functional issue?

    Thank you.

  • For 0 to −0.5 V, there will be no issue.
    According to the ISIS model, for 0 to −0.95 V, there will be no issue.

  • Thank you for very quick response.

    I understood.