An electrical device like this requires a reverse leakage current of 100nA @ 21V.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).
SMMSZ5254BT1G Features
reverse leakage current of 100nA @ 21V 100nA @ 21V is the maximum voltage (Tol)
SMMSZ5254BT1G Applications
There are a lot of ON Semiconductor SMMSZ5254BT1G applications of zener single diodes.