MOSFET packaging

Hi,

I'am putting together a H-bridge and I have found some interesting SO-8
MOSFETs with combined P/N channels on the same chip.
The maximum power-rating for such packages seems to be 2.5W. But many of
these mosfets have a rating of several amperes continous current.

If I have a MOSFET like this with e.g. Ids continous = 4A, and Pmax=2.5W,
does this mean that Vds cannot be larger than 2.5/4 = 0.62V ?

Am I right to say that the ampare rating for such MOSFETs is not relevant
for driving motors, except perhaps small lov-voltage motors with low torque
and high speed?

Now, for TO-92 or I-Pak power MOSFET the watt-rating is suddenly very high.
What MOSFET packaging would cover the usage between these extremes? For
example, I have some very small Lithium-Polymer batteries with several
amperes discharge current. If I want to drive a 3V motor with 1A current
using such a battery I would need a mosfets that can handle about 4W to be
safe. Most of the TO-92 power mosfets I see seem to be completely overkill
for this, and I also want things to be as small as possible.


erik






.

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