> So are you saying your application can not tolerate a drop of 600mV? If it
> can, I'd go with the schottky..

> Your going to get some drop with the MOSFET - In the datasheet for your
> MOSFET, it has a ds resistance of 0.02 ohm at -10V gs, 38A. 38*0.02 = 760mV
> drop (I may be wrong, but it seems this way)

Worse, Rdson data sheet specs are usually given at extremely low duty
cycles and high frequencies so that die heating times are low and
there is lots of time for cooling. This is 'extremely naughty' of the
data sheet writers as the condition is unlike most versions of reality
and, as everyone has the same issue with their MOSFETS, if all makers
used sensible values all would be better off.

Real world Rdson is usually not worse than about 2 x the pulsed Rdson.
As a rule of thumb I double quoted Rdson for quick calculations.

That's why I said that a MOSFET voltage drop "can be lower" than a
diode. It muchly deep ends on Rdson and current.

In my application that I mentioned a Schottky drop is 7% to 10% of
battery voltage and that both directly subtracts from supply
efficiency and stops you using the last 10% + of usable battery
capacity.



     Russell McMahon
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