Circuit Protection of Serial Port

Design Notes:
Protection Application:
The signals used in an RS-232 port can vary between -12V to +12V, with a maximum data rate of 256kbps. Since this is a low-speed system, the capacitance of the suppress is not a concern. The signal lines to be protected from ESD include RD, TD, RTS, CTS, DSR and DTR.
Solution Description:
As shown at the left, discrete multilayer varistors can be used for board layout flexibility, or to reduce part count, a single rail clamp device can be used.
Companion Solutions:
Other solutions within the Ruilon portfolio exist in addition to these recommendations. For example, if the signal voltages will be limited in the range from -5V to +5V, then an MLV with a lower operating voltage can be chosen.
Regulatory Issues:
The IEC 61000-4-2 will be the most appropriate standard that applies for this port. It supplies a test method for verifying that the end product is not susceptible to ESD events.
Unique Features:Does not apply.
Application Warnings:Does not apply.

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