The dynamic impedance is defined as: . When the device is operating with two external resistors (see Figure 18), the total dynamic impedance of the circuit is given by: , which is approximately equal to .
The VKA of the ATL431LI-Q1 can be affected by the dynamic impedance. The ATL431LI-Q1 test current Itest for VKA is specified in the Electrical Characteristics. Any deviation from Itest can cause deviation on the output VKA. Figure 20 shows the effect of the dynamic impedance on the VKA.