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Original question:

TCA9617A: TCA9617 - I2C Problem

TCA9617A: Putting 2 TCA9617A in series to obtain levelshifting from 1.2V to 5V

Wouter Janssens
Prodigy 10 points
Part Number: TCA9617A
Other Parts Discussed in Thread: LSF0102, TCA9406

Tool/software:

We are developing a tool to communicate I²C with a voltage level range 1.2V to 5V.  Is the setup possible to put the voltage translators in this way in series?

Will it lower our communication speed compared to 1 translation instead of 2? We are aiming FM+. The 2 TCA9617A devices are next to each other on the PCB in our communication tool.

Can you please confirm that this setup is valid?

 

Thanks

Wouter

  • 0
    Guru 316470 points

    You must not connect the B sides of two TCA9617As together.

    The simplest way to allow this voltage range is a single LSF0102, with VREFA = 1.2 V and VREFB ≥ 3.3 V. (The only restriction on the I/O pull-up voltages is that they must not be smaller then VREFA.)

  • 0 in reply to Clemens Ladisch
    Prodigy 10 points

    To understand it correctly, with the LSF0102, the FPGA signals should be 1.2V instead of 3.3V? And we can use VrefB at 3.3V and use at that side PU level to 1.2V - 3.3V? For higher voltage levels, we just need to keep VCCB the same as the PU level (3.3V - 5V)?

    On the other hand, what is the reason that you can't connect 2 B-sides to each other? Can it be solved by putting an extra device in between?

    Do you have another solution that makes it work at B-side from 1.2V to 5V with A-side 3.3V?

  • 0 in reply to Wouter Janssens
    Guru 316470 points

    No, VREFA should be 1.2 V. VREFB can be any voltage at least 0.8 V higher. The FPGA and the application device can use any voltage between 1.2 V and 5 V.

    (The LSF is a very strange device; VREFA/B are not power supplies.)

  • 0 in reply to Clemens Ladisch
    TI__Guru 50206 points

    Hi Wouter,

    In addition to Clemens' feedback, notice that the VOL for the TCA B-side is between 0.48 V to 0.58 V. This is too high for a valid VIL of 0.4 V. Hence, not recommended to connect 2 B-sides. If interested in putting an extra device in between, a device with valid VOL < 0.4 V would suffice, thanks.

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Prodigy 10 points

    Hello Michael,

    So if we replace the 1st TCA9617 by TCA9406, is this then the correct solution, looking at the Vol and Vil?

    FPGA  <-> (A) TCA9406 (B)  <-> (B) TCA9617 (A)  <->  Application

    Please advice... 

    Wouter

  • +1 in reply to Wouter Janssens
    Guru 316470 points

    This will work.

    (The TCA9406 is a passive switch, like the LSF, but it already has internal pull-up resistors, so you should not use external ones to improve VOL.)