TCA9511A: Max. Cable Length Supported

Hey Roy,

"1. When would you suggest adding an I2C buffer? When a cable exceeds a certain length?"

That's a tough question because it depends on parasitics (inductive and capacitive) as well as the bus loading. Using a cable can introduce inductive kickbacks and can damage the devices seeing the event as well as introducing more capacitance which I2C limits by 400pF for standard mode and fast mode. Both these parasitics depend on the type/quality of cable you use. If I were forced to pick a number I would say when the cable length is larger than 0.5 meters then you may need to start monitoring the I2C bus to ensure the signal integrity is intact.

"2. What's the maximum cable length supported by TCA9511A?"

The device was designed to support up to 400pF of capacitance. Max cable length depends on many factors. If we base the calculations solely on capacitance as the limit and assume a CAT5 cable (which has about 50pF per meter) then we can support 8 meters of cable (400pF/50pF=8) assuming we ignore the device's capacitance and connector capacitance. This doesn't take into account the signal propagation delays though.

-Bobby