The TCA4311 is a hot swappable I2C bus buffer that supports
I/O card insertion into a live backplane without corruption of the data and clock busses. Control
circuitry prevents the backplane from being connected to the card until a stop command or bus idle
occurs on the backplane without bus contention on the card. When the connection is made, this
device provides bidirectional buffering, keeping the backplane and card capacitances isolated.
During insertion, the SDA and SCL lines are precharged to 1 V to minimize the current required to
charge the parasitic capacitance of the chip.
When the I2C bus is idle, the TCA4311 can be put into shutdown
mode by setting the EN pin low. When EN is high, the TCA4311 resumes normal operation. It also
includes an open drain READY output pin, which indicates that the backplane and card sides are
connected together. When READY is high, the SDAIN and SCLIN are connected to SDAOUT and SCLOUT.
When the two sides are disconnected, READY is low.
Both the backplane and card may be powered with supply voltages ranging from 2.7 V to 5.5
V, with no restrictions on which supply voltage is higher.
The TCA4311 has standard open-drain I/Os. The size of the pullup resistors to the I/Os
depends on the system, but each side of this buffer must have a pullup resistor. The device is
designed to work with Standard Mode and Fast Mode I2C devices in
addition to SMBus devices. Standard Mode I2C devices only specify 3 mA
in a generic I2C system where Standard Mode devices and multiple masters
are possible. Under certain conditions, high termination currents can be used.