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TXB0106: Ioff behaviour

Giuseppe Serafini
Prodigy 30 points

Part Number: TXB0106

Hello,

The datasheet states that if VCCA and/or VCCB is unpowered, the pins of the corresponding port are placed in a high-impedance (tri-state) mode to prevent current drain.

If Vccb=0 and Vcca=1.8V, what are the state of port B pins?

If Vcca=1.8V and Vccb ramps down to 0V, what is the voltage threshold at which the I-off protection places the port B pins into a high-impedance state? During this power-down event, the condition VCCA≤VCCB is violated for a certain time.

Thank you

Giuseppe

  • 0
    TI__Guru 50361 points

    Hi Giuseppe,

    During power up, when either VCCA or VCCB is lower than min operating supply, the outputs are tri-stated. Having VCCB powered off while VCCA is acceptable here, and the excessive current leakage concern for VCCA>VCCB is more applicable during translation operation, which is further documented in this app note: www.ti.com/.../scea060.pdf

    Regards,

    Jack

  • 0 in reply to Jack Guan
    Prodigy 30 points

    Hi Jack,

    thank you about that. So when Vccb ramp down during partial power down and Vcca still for example at 1.8V it is expexted a current leakage through the Vcca power supply pin until Ioff circuit disable the chip when Vccb reaches a certain threshold. Do you know threshold value?

    Does Ioff circuit also put in 3-state I/O pins?

    Regards,

    Giuseppe

  • +1 in reply to Giuseppe Serafini
    TI__Guru 50361 points

    Hi Giuseppe,

    Note the IOFF circuitry is ensuring that the current through the I/Os when VCCA/ VCCB is powered down and the power block itself is a different circuitry. As for the leakage through the power supplies, the device prevents back leakage once VCCA or VCCB goes below the min. voltage as listed in R.O.C in the datasheet.

    Regards,

    Jack