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TCA9517: Operation when changing from low signal to high signal

Y.Ottey
Mastermind 6145 points
Part Number: TCA9517

Dear all,

Our customer ask about operation when changing from low signal to high signal.

When a low signal is input to the A side, the output on the B side of TCA9517 outputs a low signal.

Then, we think that the B side input of TCA9517 detects the low signal and outputs the low signal from the A side.

If the signal on the A side changes from this state to the high signal or the open state, we think that this device cannot drive to the high signal because the A side output of the TCA9517 outputs a low signal.

How does this device drive high?

Best Regards,

Y.Ottey

  • 0
    TI__Guru 62920 points

    Hello,

    This device is designed such that the output low level for the "B" side is about 0.5 V.  The input level required to detect a "low" level is less than this, though.  This means that the device won't recognize its own low output as a low input on the B side.  This technique of using a slightly higher "low" level is common in I2C buffers, and you can read more about it in section 9.3.3 of the TCA9517 datasheet or this application note:

    http://www.ti.com/lit/an/scpa054/scpa054.pdf

    The technique is effective for preventing a low-level "lock up" condition, but the side effect is that the "B" sides of two different devices should not be connected to one another.

    Please let us know if this is unclear or if you have any further questions.

    Regards,
    Max