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TCA9617B: I2C SDA NACK

Peiwu Ren
Prodigy 10 points
Part Number: TCA9617B


HI TI team：

In my application, TCA9617 is used as the I2C level converter(3.3V->1.8V), and the circuit diagram is as follows：

B side: Controller

A side: Target

image.png

During debugging, it was found that I2C communication is unstable. Use a logic analyzer to capture the waveform as follows：

  1. When the probe is connected to the B side, NACK occurs in I2C communication, and the retry may return to normal. 
  2. When the probe is connected to the A side, I2C communication becomes stable (even without retry).  

Why does connecting logic analyzer/oscilloscope probes on I2C bus improve communication stability? How can I fix this issue?

5686f373-6ab2-484d-a85f-152e07806f01.png

  • 0
    TI__Mastermind 42355 points

    您好

    已经收到了您的案例，调查需要些时间，感谢您的耐心等待

  • 0
    TI__Mastermind 42355 points

    您好

    你是在I2C通信期间进行探测吗？

    每个探头都有特定的阻抗和电容。在通信过程中使用示波器探头相当于连接了一个未充电的电容器，这会将总线拉低。这可能是您在SDA上观察到尖峰出现的原因。

  • 0 回复 Daniel
    Prodigy 10 points

    Yes, I captured the waveform during I2C communication。

    How can i fix it？

    Do we need to add equivalent resistance/capacitance on the SDA line？

  • 0 回复 Peiwu Ren
    TI__Mastermind 42355 points

    您好

    What I am suggesting is that the probes that you are using have some parasitic capacitance on them. 

    When you connect them during I2C communication, there will be a slight dip in the signal because you are connecting an un-charged capacitor (the scope probe) to the data line SDA. Thus it pulls SDA LOW and causes a glitch. 

    Does the communication work properly once the scope probes are attached? If so, your system is okay. It is the scope probe causing the data communication errors not your system.