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TCA9548A: I2C Bus Expander problem

Shyam Daram
Expert 1160 points
Part Number: TCA9548A
Other Parts Discussed in Thread: TCA9803, TCA9517

Hi,

I have a I2C expander input coming from two independent controllers, but effectively only one will alive at a time, below is the schematic

is it ok to tie OE directly to VCC ?

After the signal reaches the expander it try to acess multiple I2C lines

is there anything wrong with my schematic ? the I2C bridge is not responding , is it wrong to tie Adress pins directly to ground ?

kindly advice.

  • +1
    Guru 243220 points

    You must not connect the B sides of two TCA9517s together.

    Control the OE inputs so that only one is active. Alternatively, use different translators, e.g., TCA9803 with the B sides towards the controllers.

    Tying the address pins to ground is OK.

    If you want to know what happens, you have to look at the I²C signals with an oscilloscope or logic analyzer.

  • 0 in reply to Clemens Ladisch
    Expert 1160 points

    i removed/de-populated the one of the TCA9517, what i am seeing is still the bridge or mux wont respond with address 0x70

  • 0 in reply to Shyam Daram
    Guru 243220 points

    Please show an oscilloscope or logic analyzer trace if the I²C signals.

  • 0
    TI__Mastermind 23513 points

    Hi Shyam,

    Shyam Daram said:
    is it ok to tie OE directly to VCC ?

    Yes, you can tie TCA9517 directly to VCCB, or leave it open because EN pin has internal pull-up resistor to VCCB. 

    Shyam Daram said:
    , is it wrong to tie Adress pins directly to ground ?

    No. Tie address input pins directly to either VCC or GND.

    I agree with Clemens about not connecting B-sides of two TCA9517s together, as this could cause oscillation. 

    Since you have removed one of the TCA9517 and still see that the bridge or mux won't respond with address 0x70 even when A2/A1/A0  = L/L/L, then there must be a secondary issue. 

    If you are able, please answer Clemens' latest request about capturing the I2C bus. I think this information will help us to find a solution to your problem.

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Expert 1160 points

    issue resolved i2c clock line was assigned a incorrect pin FPGA side, on top of it the tieing TCA9517s together caused issue

    Thanks a ton for your prompt responses.