Hi,
I've got a situation where I can have a 9V signal present on one of the input pins of this chip when it's unpowered. I was thinking of adding a series resistor on that input, or potentially even a series resistor plus a diode from the input pin to the CD40106 rail (the idea being to use a beefier diode that I know the limits of, rather than rely on the chips internal protection circuitry).
I saw in the datasheet though that inputs already incorporate some series resistance in addition to the protection diodes (see image below for screenshot), and so I'm wondering if even any external protection is necessary? I understand that the safest option would probably be to have it, but this is an already existing board that I'll be reworking so I'd rather keep modifications to a minimum.