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TCA9509: Will I2C signals on the A side be isolated from B side if the B side is the only rail powered

Alan Hatfield
Prodigy 10 points
Part Number: TCA9509


Tool/software:

For the TC9509, we have the B side connected to 3.3V and the A side connected to 1.8V.  During power on the 3.3V(side A) is powered up first.  This 3.3V voltage rail is also connected to the EN signal.  With the A side off and not yet powered, is it possible that the logic on the SCL/SDA side A could impact side B of the level shifter?  We are concerned about potential leakage of the signal on the B side from the A side.

  • 0
    Guru 318050 points

    Section 9 of the datasheet says:

    VCCB and VCCA can be applied in any sequence at power up. The TCA9509 includes a power-up circuit that keeps the output drivers turned off until VCCB is above 2.5 V and the VCCA is above 0.8 V.

  • 0
    TI__Guru 50898 points

    Hi Alan,

    See Clemens comments about the TCA9509 supporting powered-off high-impedance on the I2C bus pins. 

    The scenario that you have should not produce leakage to the other side. 

    Regards,

    Tyler