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TCA39306: The external fixed pull up in I3C bus translation for TCA39306

Danilo A.
Mastermind 33900 points

Part Number: TCA39306

Hi Team,

Posting on behalf of our customer.

I'll share this E2E post with our customer so he can reply when needed.

For the I3C bus voltage translation applying, the external fixed pull up resistors are needed according the description in 9.3.2.

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But according to I3C spec, the pull-up should be dynamic: pull-up enable in I3C push-pull mode and pull-up disable in SMBUS open drain mode, so the fixed external pull-up in the reference design should have some impact in I3C push-pull mode?

Regards,

Danilo

  • 0
    TI__Guru 57291 points

    Hi Danilo,

    We will get back to you tomorrow on this one.
    Regards,

    Jack

  • 0
    TI__Guru 61878 points

    Hi Danilo,

    I agree, pull-up should be dynamic but this device is passive and does not have the control circuitry to handle the pull-up on the output side. 

    Thus you have an MCU or processor with I3C on  the 1.8V side. When it switches to push-pull mode and drives high (1.8V), the output floats to 1.8V. You need a pull-up to 3.3V to do "drive" the output signal the rest of the way. 

    The "SW" block will enter the cut-off region when side 1 drives to 1.8V, the VEN = 2.4V = 1.8V + VTH. So the output needs the pull-up to 3.3V to get to the correct voltage at the I3C target. 

    Regards,

    Tyler