TVS diodes possess two functional modes, a high-impedance and a conducting mode.

During normal operating conditions, that is in the absence of high voltage transients, the breakdown voltage of TVS diodes is not exceeded and the devices remain high-impedance.

In the presence of high-voltage transients the breakdown voltage is exceeded. The TVS diodes then conduct and become low-impedance. In this mode excessive transient energy is shunted directly to local circuit ground, preventing USB transceivers from electrical damage.