Ultra-low voltage, 1MHz, 8-channel I2C mux with reset

The TCA9847 device is an 8-channel, bidirectional

translating multiplexer that can be controlled through the I2C bus. The

SCL/SDA upstream pair fans out to eight downstream pairs, or channels. Any

individual SCn/SDn channel or combination of channels can be selected, determined by

the contents of the programmable control register. These downstream channels can be

used to resolve I2C target address conflicts. For example, if eight

identical digital temperature sensors are needed in the application, one sensor can

be connected at each channel: 0-7.

The system controller can reset the TCA9847 in the event of a time-out, or other improper operation by asserting a low in the RESET input. Similarly, the power-on reset deselects all channels and initializes the I2C/SMBus state machine. Asserting RESET causes the same reset and initialization to occur without powering down the part. This allows recovery if one of the downstream I2C buses get stuck in a low state.

The pass gates of the switches are constructed so that VDD1/VDD2 pins can be used to limit the maximum high voltage, which is passed by the TCA9847. Limiting the maximum high voltage allows the use of different bus voltages on each pair, so that 0.65V, 0.8V, 1.2V, or 1.8V parts can communicate with 3.3V parts, without any additional protection. External pullup resistors pull the bus up to the desired voltage level for each channel. All I/O pins are 3.6V tolerant.