A case study on ESD immunity test for a small-type control board

In conformity with the IEC61000-4-2 standard, we conducted a case study of electrostatic discharge (ESD) tests for a small-type control board to investigate the basic coupling characteristics of induced noises by indirect ESDs. With a vertical coupling metal plane (VCP) and a horizontal coupling metal plane (HCP), the test was conducted under ±4kV and ± 8kV charging voltages. Pulse width modulation (PWM) signal outputs, which were used for controlling a pulse motor, were measured with a digital oscilloscope and were statistically analyzed with respect to their pulse widths. The analyzed results show that the interference from the ESD noises could be divided into two types: the first type is a very short pulse which is caused by the ESD noise itself, while the other one is the induced pulses overlapping on the PWM signals, which are split into several short pulses by the ESD noise. This type noise may result in causing a malfunction of the pulse motor. Furthermore, from the experiment more findings could be derived as follows: Firstly, the main interference from the indirect ESDs is the first type, and the higher charge voltage an ESD gun has, more frequently both types appear. Secondly, no matter which polarity induced noise voltages from the ESD gun have, both types of interference can be observed. Finally, the interference from the HCP is stronger than that from the VCP.