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TCA9406: rising edge waveform abnormal

Ting Zeng
Prodigy 20 points
Part Number: TCA9406

Hi there

I found the rising edge of SDA_B and SCL_B is not monotonically decreasing when data is from B to A，The glitch also appear on SDA_A and SCL_A。FIGURE 1 AND 2 

I found only overshoot on the rising of SDA_A and SCL_A  when data is from A to B.FIGURE 3

After disconnect SDA_A and SCL_A from I2C bus, the glitch disappears.

My question is how to eliminate the glitch of TCA9406

Thanks

 

  • 0
    TI__Guru 56180 points

    Hi Ting,

    Do you have an I2C block diagram I could see? This looks like it may be due to an another I2C rise time accelerator on the bus or the device is connected to another pass FET architecture device (level shifter/I2C switch/MUX)

    -Bobby

  • 0
    Prodigy 20 points

    bobby：

    this is our block diagram ，but we bought the server and cannot know the  schematic circuit 。

    If you have some idea for me to decrease or eliminate the glitch。

  • 0 in reply to Ting Zeng
    TI__Guru 56180 points

    Hey Ting,

    Can you change the pull up resistors on both sides to be large like 20k? The device itself has a rise time accelerator (RTA) which will help the rising edge, having a 2k pull up resistor is probably triggering the RTAs sooner and may be hurting the signal integrity here. 

    After you do that, please show the waveforms again so we can verify if the pull ups were related to the issue. We may also need to add some capacitance on the bus to slow down the rising edges a bit. 

    -Bobby