Don't the MOSFETs also have a R_DS_on ? You might get a voltage drop across them too if the current is high enough...
If the current were so high that the voltage drop over the MOSFET was higher than the forward voltage of the Schottky diode, it would be the Schottky diode that passes the current.
Practical parts:
A typical part used for this would be something like DMG2305UX-7, with R
DS(ON) less than 50mOhm with V
GS(TH) = -4.5V. Even at 4A current, the voltage drop would be 0.2V. My current needs are modest, typically in the 100mA-500mA range, corresponding to a 0.005V to 0.025V voltage drop.
The DMG2305UX-7's (SOT23-3) cost 0.333€ (and 3A Schottky diodes like PMEG3030EP,115 0.369€) in singles at Mouser; making this configuration just sixty cents more expensive than just the two Schottky diodes that most circuits use. If one were to just chuck an LDO to drop the voltage to 3.3V or whatever one needs, this would not make any sense, but I intend to use something better, like TPS82084 (2.45€ in singles at Mouser; 90%+ efficient at 1mA+ from 5V to 3.3V; 94%+ at 100mA+, if TI Webench design report is accurate).
Background:
Using a Schottky diode with a 0.3V forward voltage turns 6% of the input power to waste heat. At 500mA input current, the DMG2305UX-7 drops only 0.025V and turns just 0.5% of the input power to waste heat. At 2A, that increases to 0.1V and 2%, correspondingly. In a hobbyist project like the ones I bumble with, it is really more about that waste heat in small plastic enclosures with horrible thermal characteristics, than being super efficient just for efficiency's sake.
Does that 6% matter? Well,
if I can avoid it by dropping two SOT23-3 jellybean parts that cost less than a third of an euro apiece, it would be worth it
for me. But if there are problems in using such circuits in real life, then no. This is why I'm asking.