Breakdown tolerance and clamping margin
The SMBJ8.0CAE3/TR13: Minimum breakdown voltage is 8.89V, giving a 0.89V guard band above the 8V standoff — enough margin to avoid nuisance triggering from normal rail ripple while still clamping fast. The 13.6V max clamp ensures the protected IC's abs-max rating is not exceeded on a 12V-tolerant input.
