TCA9546A: Vpass MIN/MAX

Hi Shota,

The TCA9546A switch is not designed to pull-up any of its SDA or SCL lines. This must be done by external pull-up resistors.

Vpass described as the "Switch Output Voltage" refers to the minimum bus voltage used in the channels.  

For example, when Vcc = 3.3v, the smallest pull-up voltage allowed on any of the channels is 1.9v. In this case, no channel could operate at 1.8v levels. In the case where a 3.3v master is to be connected to 1.8v slaves, Vcc to the PCA9546A could be tied to the 1.8v line (Vpass < 1v) to allow communication. 

When considering pull-up resistor values, you should take into account how many channels will be activated at a time in this system. When multiple channels are active and a device tries to pull the line LOW, all channels are essentially shorted through the pass-FETs to GND through the device that currently controls the bus. In this case, all of the pull-up resistors now act in parallel with the same bus. You must be sure that in the worst case (most channels active) case, the voltage is still below the minimum Vil of all I2C devices. 

Here's an example of this occurring with a simple 1:1 translator device:

Here's an app note on pull-up selection if you'd like more information:

I2C Bus Pull-Up Resistor Calculation

Let me know if this makes sense or you have any more questions.

Regards,
Eric