A lot of SOT-23 FET gates have built-in back-to-back Zener diodes to source, presumably to protect against over-voltage. However, the datasheets typically say nothing about the characteristics of these diodes. The gate leakage current will be much higher in FET's that have this structure (compared to those that don't), but otherwise the datasheets are silent about it.
One example: Diodes, Inc. p/n DMP10H4D2S-7.
I am designing a circuit where I am installing external back-to-back Zener diodes to protect the FET gate under certain conditions. But I am curious if I really need them or not. It seems to me that if I limit the current sufficiently, the built-in Zeners should protect the gate.
If anybody has any thoughts on this topic, I would be very eager to hear them. I mean, the obvious thing to do is just add the external protection to be safe. But I still want to know if anyone has any insight on the built-in protection.