It clamps transients on a 5V rail: reverse standoff is 5V typical, breakdown minimum is 5.6V, and clamping at peak current is 9V max. The SQ-MELF B package is a surface-mount hermetic barrel — it handles the thermal pulse of a 315A (8/20µs) surge without cracking, and it reflows cleanly with standard profiles.
Breakdown and clamping – the rail-protection numbers that matter
With a 5V reverse standoff, this part sits directly on a 5V supply rail without leakage at nominal voltage. The 5.6V minimum breakdown means it starts conducting before the rail hits 6V, and the 9V max clamp holds the transient below the absolute maximum of most 5V logic and MCU I/O. The 315A peak pulse current rating at 8/20µs waveform is the surge it can absorb once — useful for lightning or inductive-load dump events. Note that power line protection is not listed, so this is a signal or low-voltage rail protector, not a mains-side device.
Active status and sourcing through distribution
For BOM-line commitment, confirm the SQ-MELF B package footprint against your PCB layout — the barrel body is symmetrical, so orientation is set by the cathode band.