Once the desired cathode current is determined, R₁ and R₂ must be selected to determine the cathode voltage. Use Equation 2 to determine V_KA. As I_REF is 4μA maximum, the I_REF * R₁ portion of the equation is almost negligible.

Jumpers J1 and J2 can be used to select the desired V_KA and each jumper selection in J1 is denoted with the respective V_KA value. Consider that these values are only valid with R₂ = 10kΩ which can be set by connecting pins 1 and 2 of jumper J2. If R₂ is disconnected or tied to a user setting, then use Equation 2 to determine the cathode voltage values.

When setting V_KA, be sure not to exceed the absolute maximum voltage rating of 37V for the TLA431.