How can an HMI (Human Machine Delivery System) pass an ESD (Electrostatic Discharge) test?

To ensure HMI passes ESD electrostatic discharge testing, a multi-level protection system from the port to the core circuitry needs to be established. ESD energy mainly enters through the metal casing, connectors, and user-accessible components. The first level of protection is the chassis. The metal casing should be reliably grounded to provide a low-impedance discharge path for ESD current; the plastic casing must ensure sufficient air gap and creepage distance between the internal circuitry and user-accessible surfaces. The second level is the I/O ports. Transient voltage suppression devices should be placed on the signal and power lines of each external interface. For example, ESD5V0D3B can be used for low-speed signals, while low-capacitance ESDLC3V3D3B should be selected for high-speed signals.

TVS diodes such as SMBJ5.0CA can be used for power lines. Protective devices should be placed as close as possible to the interface connectors. The third level is on-board protection. For signals that may reach sensitive chips after entering from the port, resistors or ferrite beads can be connected in series, along with capacitors to ground, to form RC filters. In terms of PCB layout, the interface area should be separated from other circuits by ground planes or trenches. In terms of software, watchdog timers and state recovery mechanisms should be added to circuits that may be reset due to ESD interference. During testing, the focus is on inspecting metal components, gaps, buttons, and interfaces for contact discharge and air discharge points. By employing Eintraelectronics' multi-layered protection scheme and a well-designed layout, HMI products can robustly pass ESD tests of ±8kV and even higher levels.