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TCA9548A* LEVEL TRANSLATION

eli
Guru 13485 points
Other Parts Discussed in Thread: TCA9548A

are starting to look for parts for a new project and I need an I2C bus MUX

The CPU I use is at 1.8V levels

The devices I use are at 3.3V levels

 found the part TCA9548A that claims support level translation 

The problem is I don’t see this from the data sheet as the VIH and the VOH will not work in mixed level system

 

  1. Can you please look if this is correct?Am I missing something?
  2. Can you recommend  a different part that will do this
  3. Can I use an external level transition parts that will work with this part?

 

  • 0
    TI__Genius 16430 points
    Hello Eli,

    The TCA9548A will support level translation.

    It uses an internal network of pass-FET switches. Basically, when you connect VCC correctly (to the lowest voltage i2c bus connected to the device, even if it isn't the master)

    Then what happens, is you must have pull-up resistors on every channel of the switch, to pull the voltage to the appropriate rail.

    The only thing to note is that the VOL seen by all slaves, will be whatever the VOL is of the device driving a low. AKA: if a master pulls the bus down to only 0.4V, then all the other devices (on other channels) will see a voltage of ~0.4V (plus some small voltage offset).


    For yoru setup, you would want to connect VCC to the 1.8V power rail, and have pull-up resistors on all channels to the appropriate power rail (you can have pull up resistors on the downstream channels to 3.3V). You shouldn't have any issues with VIH. When the 1.8V rail goes high, the switch will actually "open" and then allow the pull-up resistor on the higher voltage bus pull up to 3.3V.