An electrical device like this requires a reverse leakage current of 50nA @ 18.9V.While the device is operating, the maximum voltage - Zener (Nom) is reduced to 27V.For operation, diode reaches 900mV @ 10mA at the maximum voltage - Forward (Vf).
BZX84-C27/DG/B2,23 Features
reverse leakage current of 50nA @ 18.9V 50nA @ 18.9V is the maximum voltage (Tol)
BZX84-C27/DG/B2,23 Applications
There are a lot of Nexperia USA Inc. BZX84-C27/DG/B2,23 applications of zener single diodes.