TCA4311A - Hot removal

Hello Nikolaos,

The TCA4311A mainly helps prevent corruption during hot-plugging. It does this by not connecting the two sides of the bus until it detects that both sides are idle.

With the disconnection, this does not need any additional protection for the following reasons:
1) The main corruption during a hot plug even comes from the current surge into a device that is plugged into the bus, causing a momentary "brown out" of the bus, which causes corruption.
2) In the opposite case, where a slave is already connected to the bus, and is removed, the net result should be negligible because the slave has no current flowing through it, and is essentially acting as a high-impedance device on the bus.

In the case where a slave is connecting with a master and is removed from the bus during mid communication (let's assume in the middle of transmitting a 0), there will be a relatively low amount of current flowing through the slave to ground (typically < 2 mA). Once the slave is removed, this current path will be removed, causing the parasitic inductance in the line to try to undershoot the voltage on the line. Normally, this is offset by the parasitic capacitance of the bus, and there is virtually no glitch on the bus, other than the signal suddenly going high. Depending on when this happens in the actual databyte, such a signal could be interpreted as a STOP condition, causing the bus to 'reset', or it could result in data being corrupted or incorrectly received, but typically, an error is generated by the lack of an ACK from a slave, and the data is disregarded.

The short answer: I2C bus does need protection during hot-plug events, mainly to prevent slaves from pulling the bus low during a potential transaction. In the reverse case, the slave itself does not have the ability to affect other communications during a removal event, simply because slaves will be in high impedance mode during another module's communication. In the event the slave is communicating while removed, then an error will likely be generated due to the lack of an ACK or a time, or data will be corrupted.