The TCA9617A 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 TCA9617A 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 TCA9617A 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 TCA9617A from being used in series with another TCA9617A 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 TCA9617A 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 TCA9617As 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 TCA9617As 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 TCA9617A 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 TCA9617A internal circuitry and all I/Os are powered by the V_CCB pin; however, due to ESD protection requirements on the SCLA and SDAA, V_CCB is required to power-up prior to V_CCA. IF SDA and SCL (on A-side or B-side) are pulled up to a positive voltage before V_CCB is powered, there can be significant current leakage into the SCA and SCL pins that can cause them to be pulled down. The SDA and SCL lines shall not be pulled up to a voltage higher than V_CCB, even when the device is powered down.

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.