What this TRANSIL TVS diode does on your rail
The STMicroelectronics 1.5KE6V8A is a unidirectional TRANSIL TVS diode in the 1.5KE series, designed to clamp transient overvoltages on a 5.8 V nominal rail. It is a through-hole device in a DO-201AA / DO-27 axial-lead package, rated for 1500 W peak pulse power per the 10/1000 µs waveform. The breakdown voltage starts at 6.45 V minimum, and the clamping voltage is held to 13.4 V maximum at the rated peak pulse current of 746 A (8/20 µs). This part is a general-purpose transient suppressor for industrial power supplies, telecom line cards, and automotive load-dump protection where a single unidirectional channel is sufficient.
For a 5.8 V rail, this translates to a clamping voltage of 13.4 V at the peak current — the load sees that voltage during the transient. If your downstream circuitry is rated for 16 V or higher, this part provides adequate margin. The capacitance of 9500 pF at 1 MHz is high enough to distort fast data lines — this part is not intended for high-speed signal protection, but for power rail and low-frequency I/O.