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TCA9544A: There are steps in the rising waveform

Shinichi Inoue
Guru 21646 points
Part Number: TCA9544A


Dear Specialists,

My customer is evaluating TCA9544A and has a question.

I would be grateful if you could advise.

---

A step was observed in the rising edge of the I2C1_SCL (TCA9544 pin 18) and I2C1_SDA (TCA9544 pin 19) signals.
*This signal is driven by the CPU's open drain output.

*SD0/SC0 is selected when checking the waveform.
*The end of PCA9615 in the latter stage is not connected.
*The same phenomenon is occurring in multiple cases.

Could you please let us know what caused this phenomenon?

What is the solution?

ch1: SCL, ch2:SDA  

Application Circuit.pdf

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I appreciate your great help in advance.

Best regards,

Shinichi

  • 0
    TI__Guru 72751 points

    Hi Shinichi,

    Are there any other I2C devices on the bus? This looks a device with a rise time accelerator could be on the bus. It also looks like there could be noise coupling onto the signal. Does this appear on all of the rising waveforms?

    Do you have a schematic we can review?

    -Bobby

  • 0 in reply to BOBBY
    Guru 21646 points

    Hi Bobby,

    I could obtain the customer’s feedback.

    ① An STmicro CPU (STM32F405) is connected as an I2C master.
    The port is PB8/9.

    *We have confirmed on the actual device that this port is set to open drain and that it operates properly as an open drain when the circuit we sent is not connected.

    ② Stepping can be seen on all rises.

    The schematic is confidential.

    Could you please send a friendship request.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    TI__Mastermind 47328 points

    Hi Shinichi,

    If the schematic is confidential, you can send it to my work email here t-townsend@ti.com 

    We can take the discussion offline and avoid the public forum altogether. 

    Regards,

    Tyler