I met a strange problem when I use PCA9518 as a I2C hub, The voltage on SCL0 and SDA0 are raised after power on, but when they are close to 0.8V, they begin dropping, and then raise again, until 3.3V, but the output such as SCL1,SDA1... looks well at the same time.
I tried several pcs of PCA9518, but got the same result, and when I moved PCA9518 from the PCB, I find the SCL0 and SDA0 signals from master are OK.
Does anyone who met the same problem before or know which reason can cause this problem, the SCL0 and SDA1 are both pull up to 3.3V through a 4.7K resistance.
Thank you very much!
Today you do the things others don't do, tomorrow you can do the things others can't do.
What you are seeing is the normal operation of the PCA9518 that occurs as a consequence of ensuring that the bus does not lock-up during operation. As the bus begins to rise it is first held at roughly 0.5V until an internal condition is met. Once the condition is met the bus is released and can rise to VCC. The 800mV peak that you see is simply an expected overshoot as the bus originally starts to rise. I attached a picture from the PCA9517 datasheet (another I2C buffer) that illustrates this situation better than the PCA9518 datasheet.
Hopefully this helps-Chris
Thank you very much for your kindly help.
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