The TCA9617B is a BiCMOS dual bidirectional buffer intended for I²C bus and SMBus systems. As with the standard I²C system, pull-up resistors are required to provide the logic high levels on the buffered bus. The TCA9617B has standard open-drain configuration of the I²C bus. The size of these pull-up resistors depends on the system, but each side of the repeater must have a pull-up resistor. The device is designed to work with Standard mode, Fast mode and Fast Mode+ I²C devices. The SCL and SDA lines shall be at high-impedance when either one of the supplies is powered off.

The TCA9617B B-side drivers operate from 2.2V to 5.5V. The output low level for this internal buffer is approximately 0.5V, but the input voltage must be below V_IL when the output is externally driven low. The higher-voltage low signal is called a buffered low. When the B-side I/O is driven low internally, the low is not recognized as a low by the input. This feature prevents a lockup condition from occurring when the input low condition is released. This type of design on the B side prevents TCA9617B from being used in series with another TCA9617B B-side or other buffers that incorporate a static or dynamic offset voltage. This is because these devices do not recognize buffered low signals as a valid low and do not propagate the signal as a buffered low again.

The TCA9617B A-side drivers operate from 0.8V to 5.5V and do not have the buffered low feature (or the static offset voltage). This means that a low signal on the B side translates to a nearly 0V low on the A side, which accommodates smaller voltage swings of low-voltage logic. The output pull-down on the A side drives a hard low, and the input level is set to 30% of V_CCA to accommodate the need for a lower low level in systems where the low-voltage-side supply voltage is as low as 0.8V.

The A side of two or more TCA9617B can be connected together to allow a star topology, with the A side on the common bus. Also, the A side can be connected directly to any other buffer with static or dynamic offset voltage. Multiple TCA9617B can be connected in series, A side to B side, with no buildup in offset voltage with only time-of-flight delays to consider.

The TCA9617B includes a power-up circuit that keeps the output drivers turned off until V_CCB is above 2V and V_CCA is above 0.7V. V_CCA is only used to provide references for the A-side input comparators and the power-good-detect circuit. The TCA9617B internal circuitry and all I/Os are powered by the V_CCB pin.

After power up and with the EN high, the A side falling below 30% of V_CCA turns on the corresponding B-side driver (either SDA or SCL) and drives the B-side down momentarily to 0V before settling to approximately 0.5V. When the A-side rises above 30% of V_CCA, the B-side pull-down driver is turned off and the external pull-up resistor pulls the pin high. If the B side falls first and goes below 0.4V, the A-side driver is turned on and drives the A-side to 0V. When the B-side rises above 0.45V, the A-side pull-down driver is turned off and the external pull-up resistor pulls the pin high.