TCA9539 Low-Power I/O Expander Texas Instruments TCA9539 Low-Power I/O Expander is a 24-pin device that provides 16 bits of general purpose parallel input and output (I/O) expansion for the two-line bidirectional I2C bus or SMBus protocol. The device can operate with a power supply voltage (VCC) ranging from 1.65V to 5.5V. The TCA9539 supports 100kHz (I2C Standard Mode) and 400kHz (I2C Fast Mode) clock frequencies. I/O expanders, like the TCA9539, provide a simple solution when additional I/Os are needed for switches, sensors, pushbuttons, LEDs, fans, and other similar devices.