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TCA9548A: TCA9548A & TCA95416A Series connection violation

Leo Chow
Expert 3120 points
Part Number: TCA9548A
Other Parts Discussed in Thread: PCA9515

Hi,

may i know if i'll be violating Vil & Vol conditions if TCA9546 & TCA9548 were being connected in series? My connection will be as follows as i'm attempting to increase number of slave devices that carries identical slave address.

MCU=>TCA9546=>TCA9548=>multiple slave address(identical addresses)

There's concern on this implementation after reading through some documents from devices such as PCA9515 mentioning two or more PCA9515s could not be setup in series connection. Does this applies to TCA9548/6 family of devices as well?

Regards,

Leo

  • 0
    TI__Guru 72161 points
    Hey Leo,

    "There's concern on this implementation after reading through some documents from devices such as PCA9515 mentioning two or more PCA9515s could not be setup in series connection. "
    This device is an I2C buffer which is different from an I2C switch. A switch uses pass FET architecture to pass signals from one side to the other. A buffer actually redrives the signal from one side to the other. Because of this it needs to have digital logic to detect lows and a mechanism to prevent itself from locking itself low. Think about it, it looks for lows but at the same time it also drives low. If it drives low, it needs to know to not see its own low and drive the other side low because of it. Switches do not work in this manner so stacking them is series is possible.

    "Does this applies to TCA9548/6 family of devices as well?"
    Yes and no. It depends on the strength of your pull ups and the Rdson of the switches and the ViL of the slaves(Vcc). If you provide a block diagram of the devices and the pull up resistors and Vcc values of the bus I can likely verify but you will also need to specify how many switch channels will be on at the same time.

    In most cases using switches in series will work. The problem arises when you enable too many channels and draw a large IoL (because the signal is not redriven you must pass all the current from one side to the other.)

    Thanks,
    -Bobby