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TCA9517-Q1: Series Application Power Supply Pics

Brandon Smith1
Prodigy 50 points
Part Number: TCA9517-Q1
Other Parts Discussed in Thread: TCA9517

Hello,

If i plan to use the TCA9517 in series, to connect an I2C bus on multiple boards, is the design intent shown in figure 9 in the datasheet to use the same power source for VCCA and VCCB for all of the buffers? If i actually have different power sources, 3.3V supplies, on each board how should VCCA and VCCB be connected on each board? Should the 3.3V rail on board 1 connect to VCCA and VCCB of the first buffer and the 3.3V rail from board 2 connect to VCCA and VCCB of the second buffer.

Please note that each board does not access to the other boards 3.3V rail.  

 

Thanks,

Brandon

  • 0
    TI__Mastermind 49040 points

    Hey Brandon,

    The configuration above will work. As long as you don't Violate the Vcc rules on the device, it shouldn't be a problem if the Vcc is powered off different rails. Just make sure you have common ground. If one side of the device is not powered up but the other is, the device will just be high impedance.

    One major note to observe:

    All B sides of TCA9517 are not to be connected to any other B side. If you accidently do this, the device will not work (pass a logic low to the other side through a B-B connection).

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 50 points

    Bobby,

    Thanks so much for the quick reply! I just want to verify and clarify:

    • VCCA and VCCB can be powered from the same power supply?
    • If two devices are used in series and each device is powered by a different supply there will be no issues. Note: Each device will also follow the above that VCCA and VCCB are connected together.
    • You noted that it is fine if one device is not powered but the other is. By one side of the device do you mean VCCA vs VCCB? This is not happen in our situation because VCCA and VCCB are tied together. What we will have though is one of the devices in series may be on but the other may be off. Is this okay?

    Thanks,

    Brandon

  • 0 in reply to Brandon Smith1
    TI__Mastermind 49040 points

    Brandon Smith1 said:
    • VCCA and VCCB can be powered from the same power supply?
      [Bobby] Yes, assuming you don't break the Vcc rules. (VccB should not be less than 2.7V)
    • If two devices are used in series and each device is powered by a different supply there will be no issues. Note: Each device will also follow the above that VCCA and VCCB are connected together.
      [Bobby] Correct, assuming you haven't broken any rules that I mentioned like VccB minimum limit and B-B side not allowed. Do keep in mind you may not be able to use the full 400kHz frequency if you go through many devices due to propagation delays.
    • You noted that it is fine if one device is not powered but the other is. By one side of the device do you mean VCCA vs VCCB? This is not happen in our situation because VCCA and VCCB are tied together. What we will have though is one of the devices in series may be on but the other may be off. Is this okay?

    [Bobby] That is okay as our device is high impedance if one board is powered while the other board is not. No problem if you keep in mind the B-B side connections do not work and limit the boards to A-B or A-A only.

    Thanks,

    Brandon

  • 0 in reply to BOBBY
    Prodigy 50 points

    Great thanks for clarifying all of that!