The next few slides will define some of the key parameters that are important factors when selecting TVS diode arrays. Shown here is what is known as a V-I curve. This characteristic curve displays the voltage and current relationships in an ESD protector. The voltage is shown horizontally and the resulting current is shown vertically. A bi-directional device has the same characteristic curve in the positive and the negative direction, so it does not matter which way they are inserted into the circuit. Looking at the back to back Zener above users will always see a forward diode and reverse diode no matter which side is looked at. Devices with a bidirectional characteristic are more suitable for signals that swing above and below GND to ensure they are not clipped by the ESD protector. A uni-directional device has a higher turn on voltage in the positive direction compared to the negative direction. In the graph above the positive direction is the result of a steering diode plus Zener diode or approximately 7.7V. The negative direction is simply a forward biased diode or approximately 0.7V.