The dynamic impedance is defined as: . When the device is operating with two external resistors (see Figure 15), the total dynamic impedance of the circuit is given by: which is approximately equal to .
The VKA of the TL431LI can be affected by the dynamic impedance. The TL431LI test current Itest for VKA is specified on the Eletrical Characteristics . Any deviation from Itest can cause deviation on the output VKA. Figure 17 shows the effect of the dynamic impedance on the VKA.