The TCA9509 is 5-V tolerant, so it does not require any additional circuitry to translate between 0.9-V to 5.5-V bus voltages and 2.7-V to 5.5-V bus voltages.

When the B-side of the TCA9509 is pulled low by a driver on the I²C bus and the falling edge goes below 0.3 V_CCB, it causes the internal driver on the A-side to turn on, causing the A-side to pull down to about 0.2 V (V_OL). When the A-side of the TCA9509 falls, a comparator detects the falling edge and causes the internal driver on the B-side to turn on and pull the B-side pin down to ground. In order to illustrate what would be seen in a typical application, refer to Figure 5-1. If the bus controller in Figure 8-1 were to write to the target through the TCA9509, waveforms shown in Figure 5-2 would be observed on the B bus. This looks like a normal I²C bus transmission, except that the high level may be as low as 0.9 V, and the turn on and turn off of the acknowledge signals are slightly delayed.

On the A-side bus of the TCA9509, the clock and data lines would have a positive offset from ground equal to the V_OL of the TCA9509. After the eighth clock pulse, the data line is pulled to the V_OL of the controller device, which is close to ground in this example. At the end of the acknowledge, the level rises only to the low level set by the driver in the TCA9509 for a short delay, while the B-bus side rises above 0.3 V_CCB and then continues high. It is important to note that any arbitration or clock stretching events require that the low level on the A-bus side at the input of the TCA9509 (V_IL) be at or below V_ILC to be recognized by the TCA9509 and then transmitted to the B-bus side.