I've used a BUK553-100B logic level power mosfet manufactured by Philips
Semiconductors for switching from PICs - however its Rds(on) is about
0.22 ohms - higher than requested.

You could try;

Device        Rds(on)    Id      Vds   Package     Manuf.

STP50N05L      0.028     50A     50V    TO220      SGS Thomson
BUK556-60H     0.02      60A     60V    TO220      Philips Semiconductors

BUK106-50L     0.035     50A     50V    SOT-263    Philips Semiconductors

You could drive these via a 470R resistor from a PIC port pin.  The resistor
should protect the PIC from any capactively coupled spikes on the gate
when switching large currents.

Unfortunately, as you want an Rds(on) < 0.03 ohms the Id capability tends
to be large and consequently the gate capacitance is also large. This means
the turn on will be very 'leisurely'.

The BUK106 might be useful as it is temperature & overload protected and
has an output pin to flag a fault condition.

Hope this is useful,

Sean Hagan


---------------------------------------
                BIME
(Bath Institute of Medical Engineering)
bime@bath.ac.uk
---------------------------------------