What are the overcurrent protection fuse tripping time requirements for data center switch interfaces?

Overcurrent protection for data center switch interfaces requires that the tripping time of the self-resetting fuse be inversely proportional to the fault current. According to the UL1434 standard: the tripping time should be <5 seconds at twice the rated current, <1 second at five times the rated current, and <0.1 seconds at ten times the rated current. Taking the Yinte Electronics SMD2920-150-16V (holding current 1.5A) as an example, the typical tripping time for a 3A fault current is 2.8 seconds, 0.5 seconds for 8A, and 0.08 seconds for 15A. The selected fuse must also meet the I²t tolerance value of the backend chip. Ethernet PHY chips typically have a short-circuit tolerance of <1A²s. This PTC has an I²t of 32A²s at 8A/0.5s, far exceeding the chip's tolerance. Therefore, a pre-installed TVS, such as the SMBJ12A, is needed to clamp and shorten the overcurrent duration within 1μs. Actual measurements show that the combined TVS and PTC can reduce the overcurrent stress at the chip end by 85%.