The major benefit of this device is its wide VCC range. It can operate from 1.65-V to 5.5-V on the P port side and
on the SDA/SCL side. This allows the TCA6408 to interface with next-generation microprocessors and
microcontrollers on the SDA/SCL side, where supply levels are dropping down to conserve power. In contrast to
the dropping power supplies of microprocessors and microcontrollers, some PCB components such as LEDs
remain at a 5-V power supply.
The bidirectional voltage level translation in the TCA6408 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 TCA6408. The voltage
level on the P port of the TCA6408 is determined by VCCP.
The TCA6408 consists of one 8-bit configuration (input or output selection), input, output, and polarity inversion
(active high) register. At power on, the I/Os are configured as inputs. However, the system master can enable
the I/Os as either inputs or outputs by writing to the I/O configuration bits. The data for each input or output is
kept in the corresponding input or output register. The polarity of the input port register can be inverted with the
polarity inversion register. All registers can be read by the system master.