Application Design Center - Set Top Box
Circuit Protection of Serial Port
Solutions
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 Littelfuse 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.
