The first device must be a common-source stage, with a drain load resistor to the +12V rail (something like 1k perhaps). This will level convert from 5V to 12V (and invert the logic). This can then drive the second devices gate at suitable levels to actually turn it on.
This looks like the right circuit to drive a 12V 3A load for my project (LED ribbon). Can I drive the load at 2Khz (switch on/off 2000 times a second) with this circuit, without wrecking the FET?Also, are there alternatives to this circuit, e.g. a single component that integrates an equivalent of this whole circuit into it -- logic-controlled high-amperage 12V amplifiers in a single package? (even if a few dollars extra)
One thing to watch for is that Rds(on) is often quoted at less than the maximum rated drain current. Always look at the datasheet and check that Rds(on) is quoted at or above the maximum drain current that you want to switch, for Vgs = 5V or lower.
Rds(on) doesn't change much with current if the device if Vgs >> Vds and you can model it as a simple resistance.