In order to program the cathode voltage to a regulated voltage a resistive bridge must be shunted between the
cathode and anode pins with the mid point tied to the reference pin. This can be seen in Figure 27, with R1 & R2
being the resistive bridge. The cathode/output voltage in the shunt regulator configuration can be approximated
by the equation shown in Figure 27. The cathode voltage can be more accuratel determined by taking in to
account the cathode current:
Vo=(1+R1/R2)*VREF-IREF*R1
In order for this equation to be valid, TL43xx must be fully biased so that it has enough open loop gain to mitigate
any gain error. This can be done by meeting the Imin spec denoted in Electrical Characteristics, TL431C,
TL432C