Texas Instruments' 8-bit I/O expander for the two-line bidirectional bus (I2C) is designed to provide general-purpose remote I/O expansion via the I2C interface [serial clock (SCL) and serial data (SDA)]. The major benefit of this device is its wide VCC range. It can operate from 1.65 V to 3.6 V on the GPIO-port side and 1.65 V to 5.5 V on the SDA/SCL side. This allows the TCA7408 to interface with next-generation microprocessors and microcontrollers on the SDA/SCL side, where supply levels are dropping down to conserve power.
The bidirectional voltage-level translation in the TCA7408 is provided through VCCI. VCCI should be connected to the VCC of the external SCL/SDA lines. This indicates the VCC level of the I2C bus to the TCA7408.