SN74CBT3305C: Difference between undershoot voltage and powered-off protection

Hi Donjie,

Essentially the device has a clamp that prevents undershoot voltages caused when the gate voltage of the n-channel pass transistors are at ground potential, but a negative voltage on either I/O port with a magnitude greater than the NMOS VT causes the switch to conduct. The C version forces the gate voltage of the NMOS to track the negative input voltage which prevents undershoot voltages up to -2V. You can find a writeup of this on page 12 of our app note  Thus, providing protection for undershoot up to −2 V by sensing an undershoot event and ensuring that the switch remains in the proper OFF state

Overvoltage protection devices have an internal sensing block that detects when a signal violates the voltage threshold. When this occurs, the switch is opened and the signal path enters a high impedance state. We have information on this topic in a separate FAQ as well!

That being said, yes - they function similarly in the sense that they both ensure that the signal path is turned off in either event. 

Thanks!

Alex