When the TMUX646 is powered off (V_DD = 0 V) the I/Os and digital logic pins of the device remains in a high impedance state. The crosstalk, off-isolation, and leakage will remain within the electrical specifications. This prevents errant voltages from reaching the rest of the system and maintains isolation when the system is powering up:

Figure 8-1 shows an example system containing a switch without powered-off protection with the following system level scenario.

1. Subsystem A powers up and starts sending information to Subsystem B that remains unpowered.
2. The I/O voltage back powers the supply rail in Subsystem B.
3. The digital logic is back powered and turns on the switch. The signal is transmitted to Subsystem B before it is powered and damages it.

Figure 8-1 System Without Powered-Off Protection

With powered-off protection, the switch prevents back powering the supply and the switch remains high-impedance. Subsystem B remains protected.

Figure 8-2 System With Powered-Off Protection

This features has the following system level benefits:

• Protects the system from damage.
• Prevents data from being transmitted unintentionally.
• Eliminates the need for power sequencing solutions, reducing BOM count and cost, simplifying system design, and improving reliability.