Bidirectional TVS for 188V rail protection
It is a Zener-type device rated for 400W peak pulse power (10/1000µs waveform), with a minimum breakdown voltage of 209V and a maximum clamping voltage of 388V at the peak pulse current of 6A (8/20µs).
Voltage window—where it protects
Above that, the 209V minimum breakdown voltage defines where the TVS starts to avalanche. The 388V clamping voltage is the maximum voltage seen by the protected circuit during a 6A (8/20µs) surge. For a 188V rail, this window leaves roughly 21V between the rail and the start of clamping—tight enough to protect most downstream semiconductors rated for 200V or higher.
The supplier device package is SMA (DO-214AC). No exposed pad—standard two-pin diode layout.