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TXB0104-Q1: Question about Ioff and OE

NOBUO FUJIHARA
Genius 9355 points
Part Number: TXB0104-Q1

Hi team,

My customer asks about below questions regarding to functionality of Ioff circuitry and OE.

Power supply:

- Vcca = 3.3V (turned off during system sleep)

- Vccb=5V(always on)

Q1) Pull-up OE to VCCA

Customer wants to pull-up OE to Vcca so that OE being enabled automatically when Vcca is turned on.

Will it be any concern to pulll-up OE while datasheet states OE should be pulled-down to GND?

Q2) Ioff functionality

Could you provide what Ioff functionality/circuitry behave?

Does Ioff functionality mean "Disable all output port when either Vcc is switched off"?

Best regards,

Nobuo

  • 0
    TI__Mastermind 45915 points

    Hey Nobuo,

    For Q1, this will be fine, no issue.

    For Q2, Ioff circuity will disable the I/Os when one of the supplies is at 0 V. So in your case, if VCCA is being powered down to 0 V then the device will be disabled even with the VCCB being at 5 V.

  • 0 in reply to Dylan Hubbard
    TI__Genius 9355 points

    Hi Dylan,

    Thanks for your prompt support.

    May I confirm below?

    For Q1, datasheet states as follow:

    "To ensure the high-impedance state of the outputs during power up or power down, the OE input pin must be tied to GND through a pulldown resistor and must not be enabled until VCCA and VCCB are fully ramped and stable."

    During Vcca ramping up, is there any concern that device connected Vcca side is exposed to Vccb level?

    For Q2, can I think that Ioff functionality is just to disable built-in output buffer shown in "8.2 Function Block Diagram"?

    Best regards,

    Nobuo

  • 0 in reply to NOBUO FUJIHARA
    TI__Mastermind 45915 points

    Hey Nobuo,

    No, Vcca will not be exposed to the Vccb level. Yes, that is a good way to think of it.