I'm using an at90s1200 output line to switch the gate
of a N-channel enhancement mode mosfet (VN2222L) to
drag a 12V line at the source down to the drain at ground.
The current going through the mosfet source to drain is
about 20mA in this automotive app, so there is no current
limiting resistor in that path since the mosfet can
handle about 200mA.
This little device is really easy to turn on when
driven directly from an atmel output pin.. too easy
in fact. The gate acts sort of like a capacitor and
keeps it's charge. Without using a pull-down resistor at the
I/O pin, the mosfet doesn't always switch off
when the I/O pin is given a logic low.
So I just guessed with a 10K pulldown resistor, and things
seem to work fine. The mosfet performs it's duties
when I set the output high, and the load shuts off
when I set it back to zero.
But can anyone comment on the merits of using higher or
lower values for a pull down in this case? I would like to
give the gate as much juice as the atmel has to offer
to turn it on, but at the same time be sure it turns off
when "let go".
The specs for VN2222L are found at
I just don't know how to interpret all the graphs
at the bottom.