Bidirectional TVS Zener — what the ratings decide
The 1.5SMC6.8CA_R1_00001: Bidirectional polarity — the CA suffix means it clamps both positive and negative transients, so it protects AC signal lines and rails where the protected node can swing below ground without forward-biasing the TVS into conduction. 5.8 V reverse standoff is the working voltage below which the device idles off-state — the protected rail should sit at or below this value in normal operation. Breakdown kicks in at 6.45 V minimum, meaning there is roughly 0.55 V of headroom between nominal standoff and the onset of conduction.