Effect of Different Load Impedances on ESD Generators and ESD Generator SPICE Models

The electrostatic discharge (ESD) generator calibration described in IEC 61000-4-2 (2008) only specifies contact mode discharge waveforms for the discharge-into-ground scenario. However, the actual device under test input impedance often differs from a short. To study the effect of different load impedances, a test method for ESD generator discharge under different load impedances is proposed. The method only slightly modifies the present calibration setup. The data show that the peak current variation between different brands of ESD generators for nonshorted load impedances is within the tolerance range given by the standard for the peak current. On the other hand, when performing system-efficient ESD design simulations, the load impedance seen by the ESD generator models is also different than a short. Therefore, the discharge current of a variety of ESD generator models is simulated with different load impedances and compared with ESD generator measurement results, which allows the selection of a suitable ESD generator model.