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TCA9548A: TCA9548 Cascading

K.Hamamoto
Guru 12155 points
Part Number: TCA9548A

Hi

Our customer is going to cascade the TCA9548A for 54 slaves. ( TCA9548A --> TCA9548A x 7 = 54 (2ch unused.) )

For this configuration, I referred the following post. 

https://e2e.ti.com/support/interface/i2c/f/390/t/535289

Then I have some additional question.

 1. Regarding RESET pin, the each RESET pins can be tied together?

 2. If so, does the pull-up resistor need?

 3. If there are unused CH, can we leave these pins open?

 4. On the above post, it is mentioned that "Make sure that you do not exceed the IOL specification that is listed in the datasheet. With more devices, you can expect this value to be higher."

     How can we calculate the total IOL if it is cascading?

Regarding,

Koji Hamamoto

  • 0
    TI__Mastermind 20905 points

    Hello Hamamoto-san,

    I have answered your questions below:

    1)  Yes, the reset can all be tied together.

    2)  It is not "required" but it is a bad habit to leave a CMOS input floating.  We recommend having a pull up resistor so that the default state is not RESET.

    3)  We generally recommend that unused channels have a week pull ups (~100k Ohms) to Vcc.  This insures that if that channel is inadvertently turned on it will not adversely affect the devices that are connected to that bus.

    4)  You will have to calculate the voltage levels seen at the slave assuming all the pull up resistors, pass FET resistances, and Device pull down resistance (pull down FETs resistance).

    You may want to consider putting buffers too.  Just imagine that all the pass fets have a resistance and can affect what ultimately will be seen at the slave device.  Will you be controlling the switches and toggling between channels or all of them be on simultaneously?  I have a lot of concerns if you plan to turn on all the channels at once.

    -Francis Houde

  • 0 in reply to fhoude
    Guru 12155 points
    Hi Francis-san

    Thank you very much for your support.

    Regards,
    Koji Hamamoto