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TCA 9548A BUS TRANSLATION

eliot steinberg
Prodigy 100 points
Other Parts Discussed in Thread: TCA9548A

Hi,

I would like to know if the TCA9548A can do  bus translation with a 3.3 volt bus on the primary side (SDA, SCL)  and 1.8 volt buses on the secondary side ((SDx, SCx).

If it will work in this application, should the VCC voltage be 1.8 volts? What should be the values of the pullup resistors on the primary and on the secondary side?

Thanks,

Eliot

  • 0
    Prodigy 100 points

    Hi,

     

    Can anybody help me with this query?

    Thanks,

     

    Eliot

  • 0 in reply to eliot steinberg
    TI__Intellectual 2020 points

    Hi Eliot,

    The Vpass needs to be less than or equal to the least bus voltage, in this case 1.8V

    Using the graph above you can see that VCC must be less than or equal to ~2.7V this means that 1.8V can be used as VCC.

    To determine the values of pull-up resistors on either side of the device, you will need to ensure that you don't violate the maximum allowable rise time for I2C.
    This will be a little more difficult due to the nature of the I2C switch and the different VCC values.

    What is the maximum number of channels do you plan to enable at one time on the TCA9548A or are you just going to enable one channel at a time? With this information, I can help you determine the best pull-up values.

    Regards,
    Chris Kraft

  • 0 in reply to Chris Kraft
    Prodigy 100 points

    Hi Chris,

    Thanks for your response. I assume, then, that I can connect SDA,SCL to a 3.3 v bus and SD(7..0) and SC(7..0) to a 1.8 v bus, using a VCC of 1.8v.

    Regarding the resistors, I actually would like the option of  communicating with the secondary buses one at a time or to all 8 of them simultaneously. If this is difficult I can get away with communicating  with them one at a time. I would appreciate your assistance in choosing the resistor values for both the primary and secondary buses.

    Thanks again,

    Eliot