What this TVS diode protects and how it clamps
The STMicroelectronics SMBJ13CA-TR is a bidirectional Zener transient voltage suppressor from the SMBJ TRANSIL™ series, designed to clamp overvoltage transients on a 13V nominal rail. The 13V reverse standoff voltage means the protected line can operate at up to 13V DC without the diode conducting; when a transient exceeds the 14.4V minimum breakdown voltage, the TVS clamps the surge to a maximum of 21.5V while shunting up to 29A of peak pulse current. This part is intended for general-purpose overvoltage protection on power supply rails, data lines, and I/O ports in industrial, telecom, and consumer equipment.