ESD / Surge couples through the winding

   
 

Xmultiple's Engineering Department


Ethernet ESD/Surge Compliance

Summary

A key requirement of Ethernet systems is immunity to transient overvoltage and surge events. These events can be caused by inductive coupling of external lightning events or simply by static electricity buildup on the Ethernet cabling. The discharge of this energy into semiconductor devices can easily become destructive. Typically, expensive and ruggedized external components such as sidactors or transient voltage suppression (TVS) diodes are added to shield silicon-based devices from the stress of external ESD/surge events. These components are often selected by trial and error to achieve the required performance. The objective of all surge techniques is not to block the surge event, but rather to enable a low impedance safe discharge path back to earth ground. These protection circuits are intended to limit stray surge current from passing through sensitive circuits, such as the Ethernet PHY device. At the same time, the protection circuit itself must be carefully designed to ensure that during these surge events (some of which have very high dv/dt), where currents can sometime be as high as 30A, that voltages do not exceed critical device breakdown so they themselves are not destroyed by the event. In many instances, designers of integrated circuit have limited tools to address what may happen at exceedingly high current levels associated with ESD/surge events. Xmultiple engineers test our connectors components with voltage and/or thermal overstress to see the point which will damage the Phy and other devices.

Magnetic Transformer schematic - Surge relevance

Xmultiple engineers have created a detail simulation/analysis model of the components involved in our magnetic transformer connectors for measurements. The Ethernet interface illustrated here is the PHY is an open drain NMOS devices. When the voltage reaches a critical level, the NMOS device will snapback. This snapback device is not a well controlled device, but rather a parasitic device with strong process dependence. This device will fail if there is enough current pushed through it for a sustained duration. Because of core saturation of the transformer, the surge energy transferred to the PHY is limited to the interwinding capacitance of the transformer. The typical interwinding capacitance range is from 5-15pF. During the strike, this charge is shared between the striking capacitor and the interwinding capacitor, and hence only 5-10% of surge energy goes through to the Phy side. The leakage inductance of the transformer helps slow down the transient waveform, however transferred surge energy is generally sufficient to cause destructive damage.

Compliance Lab Test Results Test of Transformer

Air Discharge IEC61000-4-2 - Pass กำ11kV
Cable Discharge Equivalent - Pass กำ8kV


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