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TCA9555: Does it have concern to use multiple pcs TCA9555

Terry Hu
Intellectual 2310 points
Part Number: TCA9555
Other Parts Discussed in Thread: TCA9617B

Tool/software:

Hi Team,

Note that TCA9555 can support up to 8pcs on a same BUS.

Could you please help to advise if there is any concern to use multiple pcs of TCA9555 on a same I2C BUS? For example using 5pcs of TCA9555 to expand 80 GPIO ports, any concern?

One concern I have is the capacitance of TCA9555 as well as the PCB trace on SCL and SDA. But we can use a I2C buffer like TCA9617 to solve this problem if the capacitance is too high, correct?

Is there any other concern beside the capacitance?

Best regards,

Terry

  • +1
    Guru 288480 points

    A very rough estimate of bus capacitance is 10 pF per device, and 1 pF/cm for traces. Five devices should not come near the 400 pF limit, but you can indeed add a buffer, if needed.

  • +1
    TI__Mastermind 34183 points

    Hi Terry,

    This is a very common application. 8 x TCA9555 on the same bus should not be a problem since A2/A1/A0 offers 2^3 = 8 unique i2c addresses. 

    According to Clemens, this is a good rough estimate of parasitic bus cap. We are looking at about 80pF from the TCA9555, plus any additional trace capacitance at 1pF/cm. If only 5 devices are used, this is even better. I don't believe a TCA9617B will be necessary here. 

    I don't know of any other concern at the moment, given your current implementation.

    Regards,

    Tyler